the Eastern Portion of the Basaltic District of India. olS 



Relative Age of the Laterite and Trap. 



I shall conclude this paper by one or two remarks on the relative age of the 

 Laterite and Trap. Dr. Babington* and Dr. Christie had observed this rock, 

 both below and above the ghats in the latitudes of Seringapatam and Goa, 

 and I have traced it in the deep and narrow valleys of Coorg, at various heights^ 

 from the level of the sea to several thousand feet above it; but as in all those 

 places it rests on syenite or other granitic rocks, from the decomposition of 

 which, in situ, there is much reason to suppose that this remarkable formation 

 is derived, no inference as to its age can be drawn from these facts. At Col- 

 ter, however, and other places on the coast of the great basaltic district, it 

 rests on the basalt, forming the summits of the hills, or an external layer over 

 the trap which constitutes the body of the hill. This superposition is exhi- 

 bited in ravines passing through the laterite, or where that rock has thinned 

 off so much, that it can be separated from the basalt below, which has most 

 commonly a stratified arrangement, often highly inclined and parallel to the 

 precipitous face of the hill. It has also been observed above the ghats, and 

 in the table-land of the Deckan, between the Godavery and Manjera rivers, 

 resting on basalt ; it is therefore probable, that the trap has been protruded 

 from below since the laterite assumed its present form. It would be improper, 

 in this place, to enter into any details regarding a formation which extends 

 over much of the Malay peninsula, Ceylon, the coasts of Coromandel and Ma- 

 labar, and Central India. In different portions of these vast countries, several 

 varieties of this rock are met with, well deserving of attention, yet its general 

 character and composition is the same over 30 degrees of longitude and 20 of 

 latitude, and nowhere is any proof to be found of its being of volcanic 

 origin t, or the equivalent of certain European rocks, as supposed by Elie de 

 Beaumont. Under the name of laterite, however, very different rocks have 

 been included ; such as the ferruginous clays and sandy beds underlying the 

 alluvium of the Irawady, near Rangoon, and a ferruginous conglomerate now 

 forming in many places from decomposed and reconsolidated laterite or 

 syenite, and containing fragments of granite, and occasionally enveloping a 

 recent land shell. 



Besides these, a rock, apparently of igneous origin, has been occasionally 

 confounded with laterite, and in the diamond districts is known to the natives 

 by the same name as is applied to that rock in the Mysore. The thinner strata 

 of the diamond sandstone of the Pennar have been observed to be bent in a 

 remarkable manner by the intrusion of this rock; and in other instances it 



* Geol. Trans., 1st Series, vol. v., p. .'329. 



t Calder, Asiatic Researches, vol. xviii. Conybeare, Report to British Association. 



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