Soils consist of mechanical mixtures and chemical compounds of the materials found on the surface of the earth. They contain both inorganic and organic materials. The process of soil formation is influenced by the physical and chemical characters of the parent rock, physiography, altitude, climatic condition and plants and animals of the surrounding region. In North East India the above factors vary from place to place. For example. the parent rocks of Meghalaya and Karbi Anglong, which are mostly metamorphic, differ from those of hills and mountains, which are sedimentary. So far physiography is concerned there are very high mountains and hills, plateaus, deep gorges and valleys and wide plains dotted with water bodies and swamps. Climate also varies according to the location and situation of the places. There are hot and humid areas, cool hilly areas and very cold glaciated areas. Similarly the plant and animal life also varies from place to place. As a result of all these different types of soils generate in different part of the region.

Soil Formation : The generally heavy rainfall, high relative humidity and high temperature cause rapid weathering of rocks of North East India. As the weathering of the surface rocks of the hills and mountains proceeds, the sheet floods caused by heavy rainfall remove the weathered materials and carry then down to the head- streams of the rivers. The rapidly flowing water of the streams then carry the sediments, big and small, down to the foothills and plains. The sediments thus are spread over large areas in the foothills and plains. Such soils are known as transported soils or azonal soils . On the other hand the summits and slopes of the mountains are left with only a thin layer of soils formed due to local weathering, These soils are known as residual soils or zonal soil. The transported soils found in the region may be divided into two groups : allivium and diluvium and colluvium. The alluvium or alluvial soils are made of made of finer grains like fine sand, loam and silt. Alluvial soils are made of these finer materials which the running water can carry far into the plains. Diluvial and colluvial soils are found in the foothills and in beds of the narrow valleys and canyons inside a hill or mountain tract. Here the soil is a mixture of fine silt and carried by running water and cobles and pebbles deposited partly by gravitational pull and partly transported by running water. The residual soils are also divided into two groups : oxisol and altisol . Oxisols which are also known as red soils, are found at lower altitudes over the hills and mountains, while the altisols are found at medium altitude (above 1500 m- 2000m) and may be called as lateriate. Besides, there is a third category of residual soil, which may be called as Mountain Soil. This type is found at higher altitides where the soil forming process is influenced more by frosts and snowfall rather then by rainfall.

Regional distribution :

The plains of the Brahmaputra and Barak in Assam the Manipur plain and the plains of Tripura have alluvial soil. The hills of North East India have red soil over lower altitudes, and laterite soil over medium altitude, while the higher mountains have mountain soil. In Assam, therefore, we find alluvial soil over the plains, red soil in most of Karbi Anglong and North-Cachar Hills and only patches of laterite over the highest part in their hill ridges .

In Arunachal, the limited river valleys contain alluvial and diluvial soil, while all the lower hills contain red soil. The areas above 4500 m have mountain soil mixed with glacio-fluvial deposits. Meghalaya has red soil all over the hills except the higher central part where laterite is found to be present. The rocks of Meghalaya contain a higher quantity of iron and hence its red soils are brighter then the red soils of other hills. Mizoram has mostly residual soils weathered from shale. Red soils predominate the state with only thin patches of laterite over the higher ridges. While the Manipur plain contains alluvial soil, its hills have residual red soils which are sandy. Nagaland also has red soils, but these are, by and large, fine grained. Besides they seem to contain more organic and nitrogenous materials. Tripura has alluvial soils over the piedmont plains and red soil over the hills. There are a few small patches of laterites also over the higher hills of Tripura.

 Classification of Soil :

There are four major groups of soil in North -East India . These are as follows :

1. Alluvial Soil : As described above, alluvial soil is found in the river valleys and plains. This is a transported soil made up largely of silt, sand and clay. By the river sides, the alluvial soil is mostly sandy while away from the rivers it tend to be clayey. This soil is slightly acidic and rich in organic material . As this soil is made up of layers of silt deposited by running water, one can find about 10/12 layers of silt within a depth of 150 cm. The soil is characterised by a concentration of ferrous oxide ( FeO ) and aluminium oxide (Al₂O₃) in its lower layers. On the other hand silica content decreases from the top soil downward.

The alluvial soil may be divided into a few categories on the basis of its physical make up. These are sandy, sandy loam, silty loam and silty. Then again, alluvial soil is divided into new alluvium and old alluvium on the basis of period of there genesis.

The old alluvium was deposited earlier in the late Pleistocene and Sub-Recent periods. In the course of time it is raised to a relatively higher level because of local tectonic activities. This soil is more consolidated, acidic and less fertile. Further, it contains less phosphate and potash . Old alluvium is found in patches generally along the foothills In the Brahmaputra Valley there is a long patch of old alluvium along the Himalayan foothills from Kokrajhar District upto the river Subansiri of Lakhimpur district . The patch is however, criss-crossed by numerous rivers coming down from the hills. In Sonitpur district the patch of fold alluvium occurs south along the middle of the north bank plain from Dikrai river upto about Gohpur. The other patch occurs at the southern and eastern margins of the south bank plain , along the foothills of Meghalaya in Dhubri, Goalpara, Kamrup and Marigaon districts, along the foothills of Karbi Anglong, in Nagaon and Golaghat districts, along the Nagaland foothills of Golaghat, Jorhat and Sibsagar districts and along the southern and eastern foothill margins of Tinsukia districts. There are patches of old alluvium in the Semphema-Diphoma area near Kohima,along the foothills of Cachar and Hailakandi districts and along the foothills in Tripura. Old alluvium often forms distinct terraces and supports tea gardens. Only in western Brahmaputra Valley this soil is not found suitable for tea cultivation because of very low phosphorus content of it in this part.

The new alluvial soil consists of recently deposited silt and sand and is rich in organic content. Hence, this type of soil, if not purely sandy, is fertile and suitable for agriculture. This soil is generally rich in phosphate, potash, calcium, nitrogenous material and organic substances . It is less acidic and not saline. Its chemical and physical characters, however, very to some extent from place to place. New alluvium is found all over the Brahmaputra and Barak Valleys, Manipur Plain and Tripura Plain except in those areas where the old alluvium occurs. Over the hills and Plateaus this soil is confined to the narrow valley bottoms. It tends to be sandy in the immediate river banks loamy at some distance from the river beds and clayey in the areas of greater distance from the rivers . Besides, those alluvial soils which are found in the swamps and marshes contain a high quantity of putrefied organic matter and hence tend to be dark in colour. Rice, jute wheat, pulses, mustard , sugar cane, maize, etc. grow well over clayey soils. Loamy soils support finer varieties of rice, pulses, mustard and vegetables. The sandy soils of the flood plains are famous for vegetables., including potato.

2. Red Soils: Red soils are normally found on all the hill slopes and hill tops except in very high altitudes. These soils become red because of the oxidation of the iron content present in them. Red soils contain organic matter and nitrogenous material. They are also acidic but have lesser quantities of phosphate and potash. In the presence of water the red soils become sticky, while in its absence they become hard and develop cracks. Red soils may be regarded as residual.

These soils are commonly found in Meghalaya, hills of Tripura, Mizoram, hills of Manipur, Nagaland, Arunachal Pradesh and in the North Cachar hills of Assam. They are bright red in Meghalaya because of the presence of a greater proportion of oxidised iron in their parent rocks, i. e. the acidic rocks of Pre-Cambrian origin.

Although the red soils are commonly found over the hills, there are patches of these in the areas of the old alluvium also. The higher parts of old alluvium, which have not been affected by flooding and subsequent silting, contain reddish soil and are found in Darrang, Sonitpur, Golaghat, Jorhat and Sibsagar districts and the foothills of Karbi Anglong.

Red soils are suitable for growing fruits Besides, on the hills slopes these also support good crops of rice, maize and millets. If irrigated, these soils can produce cotton, rice, maize, wheat, pulses, potato, and citrus fruits, especially lemon, orange, pine apple, pear plum and grape.

3. Laterite Soil : Laterite is found only in small patches at the medium altitude of the hills. This soil contains considerable quantities of iron and aluminum and hence is hard when dry and red in colour. When wet it becomes sticky. Laterite soil contains less quantities of nitrogenous material, phosphorus and lime. It is a leached soil and hence not fertile. There are two types of laterite, viz. high altitude laterite and low altitude laterite . Both the types develop on the hill tops and slopes which have heavy rainfall, generally high relative humidity and facility for good drainage.

Laterite is distributed in small patches over higher hills tops of Karbi Anglong and North Cachar hills of Assam. Relatively extensive patches of laterite is found in the Cherrapunji region of Meghalaya over sandstone deposits.

In Manipur laterite is confined to the higher hills tops of the south-eastern region . In Mizoram and Tripura it is found on the ridges of higher altitude . In Arunachal Pradesh laterite is found in patches at mid -altitude on sand stone rocks.

Laterite is useful for growing crops only when water is supplied. Over the high altitude laterite millets and pulses can be grown well, while on low altitude laterite cotton, millets, rice, banana and citrus fruits grow well with irrigation.

4. Mountain Soil : In North-East India mountain soil is found over very high altitude (above 4500 m ). Such soil is therefore, confined to the higher altitudes in Arunachal Pradesh and over the summit region of the Patkai Range. This soil remains frosted in winter , In Arunachal this soil is mixed with fluvio -glacial deposit. Because of prevalence of low temperature, chemical decomposition is of lesser measure in the case of this soil. Hence it contains pebbles, cobbles and boulders along with sand and silt. Mountain soil is not fertile. It however. supports millets, barley and good grass for animal fodder.                          

MINERAL RESOURCES

            North East India is fairly rich in mineral resources. Apart from petroleum, coal, limestone and sillimanite, which have been regularly extracted since long, the region also has a number of other valuable minerals. The Geological Survey of India and the Department of Geology and Mining of each of the states of the region has been exploring and assessing the reserves of  various economic minerals present here. Besides, the  Oil India Limited and the Oil and Natural Gas Commission are specifically engaged in exploring and assessing the reserves of oil and natural gas  in North East India. The efforts  so far made have revealed that the region has the following minerals stored in it :

                                                  North -East India

                                       Reserves of  Some Minerals

                                               (in million tonnes)

            The above table shows the estimated reserves of the mineral so  far estimated. There are some other economic minerals whose traces have been found here and there in the region. But their reserves have not been estimated because of inaccessibility of many parts of Arunachal Pradesh, Nagaland, North Cachar Hills, Manipur, Mizoram and even Meghalaya. The minerals, whose presence has been detected in the region include copper, chromite, nickel, cobalt, fire clay, kaolin, corundum, asbestos ,gypsum, beryl, graphite, gold, mica, alum, shale and mineral salt.

            Iron Ore : The iron one deposits so far explored in the region are found to contain a low proportion (41% and below) of iron. Besides, a very large quantity of ore has also not been found to be located at one place. In spite of such drawback iron used to be mined in the North East India in the past , especially during the medieval period. It is found that during the Ahom reign iron used to be mined from the north  western foothills of Tirap and Nagaland in the areas stretching from Jaipur in the east to Tiru Pahar and Telpung in the west. The mines were located at Jaipur, Tipam, Bosadaiyang, Tiru Pahar and Telpung, The present day explorations have revealed that these areas have ironstone nodules and shale of the Tipam and Barail Series of sedimentary rocks containing from 22.1% to 40.1% of iron.

            The second area where iron ores are found lies in Dhubri district in an around the hills of Bilasipara, especially at Chandardinga hills (estd. reserve 17 million tonnes) and at Melajgarh (26⁰15� 20�N and 90 ⁰ 28�00�E) near Abhayapuri. The ores here contain 30% -40% iron. The third reserve is found in the Meghalaya foothills of Kamrup and Goalpara district at Nalanga Beel, Kumri hill, Langupara hill, Khardong and at Arandanga-Raochapra area near Hahim, In the Garo Hills district iron ore has been  discovered at Athiabari and Nichangram. In the East Khasi Hills it has been found at a place 28 km north of Cherrapunji, where magnetite is present in the granite deposits. In Nagaland Laterite cappings, rich in iron are found in the north western foothills of Wokha district. In Manipur  bog iron is present in an wide area near Lauchipat. In Arunachal Pradesh iron ore has been detected in East Kameng and West Siang  districts.

            It has, however, been found that iron content in the ores of the North East India is generally low, being less than 50% Hence no entrepreneur comes forward to set up a steel plant, although other raw materials, except manganese, are not absent in the region. But if manganese is imported, a medium steel plant or a sponge iron plant may be set up  with coking coal from the reserve of the area between Namchik and Namphuk rivers of Changlang.

            Copper : Economically exploitable copper deposit has so far not been found  in North East India. Small deposits have so far been found in Assam, Meghalaya, Nagaland and Manipur. In Assam , it has been found in small proportions at Mahamaya hills of Bagribari area of Dhubri district, Barduar area of Kamrup district and in the upper reach of the  Barjuri river in Karbi Anglong. Copper is found in these hills in the from of pyrrhotite, chalcopyrite and pyrite in small proportions of 0.04% to 0.39%. In Meghalaya it is found at Umpirtha and Ranighat (25⁰50� N,91⁰10�30� E). In Nagaland copper is present in the  basic and chalcocite. In Manipur it has been reported from Nungon, Kongal, Thana and Ningthi (Maklong Khing) area by the Geological Survey of India.

            Chromite and Some other related minerals : Chromite is rarely found in our country and more so in this region. Small deposits of chromite have  been found in Nagaland in the ultrabasic rocks situated near the Patkai Range. In Manipur it has been found at Siroi hill of Ukrul and Moreh of Chandel district. In Meghalaya chromite has been found in the  Sizu basin and in Arunachal it is discovered at Tiding Valley.

            Besides the above minerals, traces of the deposits of nickel, cobalt, gold, silver, lead, molybdenum, platinum, iridium and germanium have also been found in North East India.

            Traces of nickel deposits have been found at Moreh, Vungon, Kongal, Thana and Ningthi areas of Manipur in association with the ultrabasic rocks and serpentine bodies. This mineral has also been traced in Subansiri district of Arunachal Pradesh. Traces of cobalt deposits have been found in the Lower Subansiri district of Arunachal and at Pulphur village in Kiphire sub-division of Tuensang district (Nagaland). Alluvial or placer gold used to be extracted from several rivers of Assam in the ancient and mediaeval periods. There are references of gold of Assam in the Mahabharata, the Alamgirnama (written by Mohammad Kazim who accompanied Mir Zumla) and the writings of Jeau Baptist Traverneer and Mr. Wade. Alluvial gold was extracted from the beds of the Nadihing, Dibang, Subansiri, Dikrong and Bargang rivers. It is said that placers were derived from the auriferous quartz veins. Presence of gold has also been found near Haflong (25⁰15�N and 92⁰ 8� W) of North  Cachar Hills at Tyrsad (8 km S. W of the Mawphlong) in the East Khasi Hills district and in Manipur in the quartz veins associated with oxides and sulphides. Although the  occurrence of silver has not yet  been traced, it is said that the metal may occur at  Bar Khamti  area of Luhit district  and at Nongpoh in the Ri Bhoi district of Meghalaya. Lead is said to occur in Sadiya sub-division and Molybdenum in the granite rocks of Cherrapunjee. Both Platinium and iridium are found to be present in the gravels of Noadihing river. The presence of germanium has been detected in the coal deposits of East and West Garo Hills to the extent of 0.095% to 0.122%.

            Coal : North East India has large reserves of coal, especially in  Assam and Meghalaya. The quality of coal so far found is however, not very good in that its organic sulphur content is high (upto3%) and carbon content is relatively low. Assam is said to contain about 1000 million tonnes of coal reserve, while Meghalaya also has about 1200 million tonnes. The first coal mining in the region was started in 1865 at the Makum coal-fields under the initiative of H.B. Medlicott.

            The coal reserves found in North East India  belong to Gondwana, and Tertiary ages. But the Gondwana coal present is in disjointed than lenses along the Himalayan foothills from Bhutan Duars to Sadiya. This has not been so far exploited because of the  thinness of the seams and transport difficulties. It is the Tertiary coal that  is found in thick workable seams and, therefore, mining has developed for its extraction in several places. But their impurities, as stated above, have hindered their optimum  exploitation. The workable Tertiary coal deposits are found in the following two groups of geological beds :

            (1) Lower Tertiary deposits are found in South Garo, Khasi and Jaintia Hills and in Karbi Anglong. These  deposits were laid down in the Eocene Period (Jaintia Group).

            2) Middle and Upper Tertiary deposits of coal are found in Ledo-Jaipur-Naginimara area of Assam. These deposits were laid down in the Tikak Parbat Formation of Barail Group during the Oligocene Period.

 Distribution of Coal Deposits : The  geographical distribution of the coal reserves is as follows :

  (A) Coalfields of Assam

1. Upper Assam Region : In the  Upper Assam region coal occurs from Miao Bum in Changlang district in the east to Nichuguard at the Nagaland foothills, south of Dimapur. The important  coalfields of the region are as follows : (i) Makum Field in the Margherita area, (ii) Jaipur-Dili Fields and (iii) Naginimara Fields.

            (i)  The Makum Coalfields are located in the Burhi Dihing Valley to the east and  south of Margherita. The important mines here are located at Borgolai, Ledo (27⁰18� : 95⁰47�), Tipang and Namdang over an area of 30 km by 5 km. The coal of the  region is mostly of bituminous variety. The seams are generally thick with an average of 17 m thickness. These fields are estimated to hold 191 million tonnes of coal. Because of transportation facilities, these fields  have been worked upon since long.

            (ii) Jaipur -Dili Field is located at the Tirap foothills of Dibrugarh district between the rivers Burhi-Dihing (near Jaipur ) and Dili (headstream of Disang). The total reserve of this coal field is estimated to be about 28 million tonnes. The coal occurs here at a depth of about 100 metres. Lakadong is the main mining area here .

            (iii) Naginimara Field is located at Nagaland foothills just south of Nazira. The total reserve of this field is estimated at 10 million tonnes. The important mining centre here is Naginimara.

  2. Karbi Anglong Coal Deposits : The  coal deposits of Karbi Anglong are found in the following places.

            (i)  Longloi Deposit : This deposit is found at Longloi about 40 km west of Barpathar. The coal seam here is about 4 metres thick. However the quality of coal as such, is not very good with a high proportion of impurities present in it .

            (ii) Koilajan Deposit : This  deposit is located at  Kailajan about 28 km west-north-west of Dimapur. The quality of coal is fairly good and it  is commercially exploited for local use.

            (iii) Silbheta Deposit : This deposit lies towards the western side of Karbi Anglong , to the north of Dimapur -Nagaon Road and covers an area of 1.4 km²  .The coal is of fairly good quality and the total reserve is estimated at 15.7 million tonnes.

            Besides the above deposits coal is also found at  Dissoma and Kaliani river valleys of Bokakhat Sub-division.

            (iv) Kharbhaman Deposit : This deposit occurs on the western side of Kharbhaman Hills (26⁰02�N : 93⁰24� E ) in the south-western part of Diphu Sub-division. There is a single seam of coal extending over 0.5 km. The estimated reserve is 0.5 million- 06 million tonnes.

  (B) Coal Fields of Meghalaya

            There are rich coal deposits along the southern part of Meghalaya in the Garo, Khasi and Jaintia hills. A broad outline of the coal deposits of the state is given below:

            (i) The Garo Hills Deposits :The Garo hills has a rich reserve of fairly good quality coal The fields of this area were first explored by Bedford in 1842 and subsequently by H.B. Medlicott of the Geological Survey of India. The G.S.I. has been still continuing their exploration, besides the Meghalaya Department of Geology and Mining for locating and assessing the  extent of the mineral reserve. The important fields so far found are located at (i) Darranggiri, (ii) Rongrengiri, (iii) Harigaon, (iv) Siju Simsang Valley and (vi) Nangalbibra (25�28 : 90⁰ 42�).

              Much attention has now been given to the development of the Darranggiri Coalfield. This field lies to the north of the Tura Range, a few km south of the Rongrenggiri field. The Simsang river, flowing through this area, exposes coal seams on both of its banks. It is said that this reserve contains about 125 million tonnes of coal. The  Darranggiri field is also very rich in reserve. It is said to continue from Darranggiri to as far east as Nongstoin of the West Khasi Hills district.

            (ii) The Khasi Hills Deposits : In Khasi hills workable deposits of coal seams are found in several places, of which Langrin (Um Blay) located in the extreme south west corner of the West Khasi Hills district,  Um Rileng, 8 km south west of Shillong , Mowbeh -Larkar, 32 km south of Shillong, Mowsynram, 19 km north west of  Shella, Mowlong, Rangsanobo and Laitryngew near Cherrapunji, and Thangjinath and Lyngkerdem near Pynursla. Of all these deposits, coal is extensively mined at (i) Um Rileng mines, (ii) Mowbeh -Larkar mines and (iii) Mowlong, Rangsanobo and Laitnyngrew mines.

            (iii) The Jaintia Hills Deposits : The workable coal seams of the  Jaintia Hills are located at Jarain, 16 km south of  Jowai, Bapung, 11 km east of Jowai, Sutunga, 24 km east -south -east of Jowai, and  Lakadong, 16 km north -east of Jaintiapur. Coal is also reported to occur in the headstream region of the Kapili River.

            (C) In Nagaland Tertiary coal is  present in the basal argillaceous beds of the Tikak Parbat formation (Barail Group) of the Oligocene Period. Because of a high content of organic sulphur and indifferent coking character, this coal has not been extensively used in the iron and  steel industry of the country. Within the state, coal deposits are  found to occur in the Dikhu (Dikhou) Valley of Mon district and Changkekong -Jopukong region of  Mokokchung district. In the latter region, Changki-Chonglymsen, Waromung -Mongchem and Lakuni-Mirinpoh are the areas where large quantities of coal occurs.

            (D) Coal Deposits of Arunachal Pradesh   In Arunachal Pradesh both Gondwana and Tertiary coal deposits occur. While the Gandwana coal deposits are found along the Himalayan foothills in the west and east Kameng districts. The Tertiary coal is present in the  Namphuk and Namchik valleys of  changlang district almost in continuation to the  Ledo-Borgolai fields.

            (E) In Manipur high grade coal has not been struck so far. However Lignite deposits occur near Kongra-Waiphei Village (24⁰ 26�35� N: 93⁰ 42�32� E), about 32 km south-west of Imphal. Lignite is also found in the Tureloo Valley in the Churachandpur district of the state.

            (F) In Tripura, coal has so far been found to occur in Kailashhar area near the Tripura-Bangladesh border in the North Tripura district This coal is of Tertiary period and contains impurities like organic sulphur. However, it is  commercially exploited for local use. Tripura also has lignite deposits at Ujan -Tangong near  Hirachara tea estate, Dertuichara and   Nattinchara. The deposits are generally small and lie under considerable rock cover. These have, therefore, not been exploited so far

           (G) Although coal has so far not  been  exploited in Mizoram, it is said that the state has some reserves, especially in Lunglei district. A sample of coal found in the Phairung river valley of the district, on analysis, is found to contain 40.40% of fixed carbon 29.14% of volatile matter, 15.97% of ash 14.49% of moisture. The presence of this sample indicates that there are coal reserves in the state.

                                                  Trend of Production :