40 LAKE : GEOLOGY OF SOUTH MALABAR. 



This view appears to have been adopted by C alder in his General Observations 

 on the Geology of India. He calls the laterite "a contemporaneous rock associat- 

 ing with trap, "' but does not enter into the question of its origin. 



Dr. Benza, 2 in his account of the Geology of the Nilgiris (1835, l ^3^>)> describes 

 what he calls hnsmatitic iron ore, which he says is often like laterite. But he does 

 not consider it a true laterite. He describes the formation of lithomarge by the 

 decomposition in situ of gneiss. He divides lateritic rocks into three groups, but 

 his definitions of these groups are not very clear. 



In a letter to Cole 3 he expresses the opinion that laterite has resulted from 

 the decomposition of granitic and other crystalline rocks. 



In 1836 Cole 4 gave a resume of the earlier papers on the subject of laterite 

 and described, from his own observations, the laterite of the Red Hills near 

 Madras. From the presence of pebbles of sandstone and crystalline rocks in this 

 laterite he concludes that it is a mechanical deposit. He does not consider the 

 evidence in favour of Voysey's views satisfactory. 



The next writer who enters into the question of the origin of laterite is Dr. J. 

 Clark 5 (1838). He considers laterite and lithomarge to have been formed, both 

 in the same way, by the decomposition in situ of gneiss ; and he thinks it probable 

 that lithomarge has been derived from a rock composed chiefly of hornblende and 

 felspar, while laterite has been derived from rock containing more quartz. He 

 divides lateritic rocks into three classes — (1) lithomargic, (2) quartzy, (3) detrital. 



R. Baird Smith 6 (1840-41) agrees with Clark*s views and gives examples of 

 this mode of formation of laterite. 



The question of the origin of laterite is ably discussed by Capt. Newbold in 

 his various papers on geology. The fullest account of his views is given in his 

 Summary of the Geology of Southern India (Journ. Roy. As. Soc, VIII, IX, 

 XII). He dismisses Voysey's theory that it is of igneous origin, on the ground 

 that " no decided volcanic product has been discovered in laterite, no crater or 

 other proof of such origin." 7 Occasionally, it fills pre-existing chinks in subjacent 

 rocks, but it never enters as a vein injected from below. With regard to the theory 

 that laterite is nothing more than granitic and other rocks weathered in situ, he 

 contends that at the Red Hills near Madras, where the laterite rests on granite, 

 it contains fragments of sandstone ; and at other places beds of lignite, &c, occur 

 interstratified with it. He examined many beds resting on trap containing chalce- 

 donies, but did not detect in the upper or middle beds of the laterite any frag- 

 ments of these chalcedonies. Laterite sometimes rests on limestone without con- 

 taining any traceable lime. 



He concludes that the rock is of aqueous and mechanical origin. On the 

 Western Ghats and on the West Coast, rocks containing much iron weather into 

 ferruginous clays that resemble laterite, and when laterite is near, appear to pass 

 into it. But Newbold does not consider these clays to be true laterite. 



1 As. Res. XVIII, 4. 



2 Mad. Journ. Lit. and Sci., IV, 241. 



3 Loc. cit., 108. 



4 Loc. cit., 100. 



3 Mad. lourn. Lit. and Sci., VIII, 334. 

 « Calc. Journ. Nat. Hist., I, 188. 

 ' Journ. Roy. As. Soc, VIII, 237. 



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