The Rajasthan desert or the Thar is another expanse of the Pleistocene and Recent deposits. While most of its sand is of Aeolian origin, a part of it is also obtained through the disintegration of the crystalline rocks there. Some sand and salt particles are also brought by the pre veiling south-west monsoon winds from the Rank of Kachchh.
The sand is deposited as vast sheets or as mounds called sand dunes. The sand largely consists of quartz with grains of feldspar and hornblende. The sand particles are uniformly rounded by attrition (V.C. Misra, 1968, p. 247). There is but little rainfall in Rajasthan-the mean annual fall being not more than 12 cm-and consequently no water-action to carry off the detritus to the sea, and hence it has gone on accumulating year after year.
The Rajasthan desert is of recent origin. There is evidence that the region north of the Kachchh and south of the Punjab was a fertile and forested tract housing flourishing cities, even so late as the time of invasion by Alexander the Great (323 B.C.). The growing aridity accompanied with excessive loss of vegetation promoted the growth of the desert. The desert is gradually encroaching upon the fertile agricultural lands of the north and the east which calls for effective counter measures to check its advancement.
The Karewas of Kashmir
The term Karewas refers to all those flat- topped mounds that border the Kashmir valley on all sides. These are composed of fine salty clays with sand and boulder gravel. Al places they contain peat and phosphate beds with mammalian fossils. Karewas are of lacustrine origin formed at a time when the entire valley was an extensive lake during the early Pleistocene period. But part of the Karewas is of glacial origin containing moraine deposits According to Midlist the thickness of Karewas goes to I4(X) m. In fact the deposits have been elevated, dissected and in a great measure removed by sub aerial denudation as well as by the Jhelum River giving them their present position.
Late rite
Late rite is a kind of vesicular calyey rock composed essentially of a mixture of the hydrated oxides of aluminium and iron with small percentage of manganese and titanium oxides. It is usually brown or reddish in colour with yellow patches due to the variable amounts of iron oxide present in it. The lighter ones are aluminous in composition while darker are ferruginous and manganifcrous. The late rite is a porous or spongy rock. When newly quarried it is soft but becomes hard and compact on exposure to the air.
Late rite is found capping the summit of the basaltic hills and plateaus of the highlands of the Deccan, central India and Madhya Pradesh. The height ranges from 600 m to 1,500 m and the thickness of the rock varies from 15 to 60 m. Isolated patches of late rite occur in Rajmahal hills (Jharkhand), Sri Lanka and Myanmar.
Late rite is divided into two forms, viz., the high-level late rite, and the low-level late rite. The former occupying the summits of hills and plateau is believed to be formed in situ. It is purer and more homogeneous in character free from gritty matter. The low-level late rite is of detritus origin and is derived from the fragments of the former and deposited near the banks of the streams and the sea coast.
Like regard late rite is the result of sub aerial weathering of crystalline and trap rocks of the Peninsula. It is believed to be the product of tropical and sub-tropical decomposition of rocks with alternating wet and dry climatic conditions. Under these conditions the decomposition of the aluminous silicates of crystalline rocks goes a step further and broken up into hydrated oxide of aluminum (bauxite). The resulting product is a mixture of bauxite, limonite and clay. The origin of late rite is attributed to physic-chemical processes in which some tropical bacteria also play some role.
Although late rite does not yield good soil due to its deficiency in salts and humus contents but is used as building material (Later-Latin meaning brick). It also provides iron ore, bauxite and manganese.
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