CXIV. PaaOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



priate, and of whicli tlie Siwalik Hills are tlie type. The Himalaya 

 or peak-rauge consists of metamorpliic and unmetamorphic rocks, 

 "while to the westward of the Beas River there is no equivalent 

 of the Lower Himalayan region. The Sub-Himalayan series is 

 divided into the Subathu group, containing Nummulites, therefore 

 probably Eocene, and the Nahun and Siwalik groups, which may 

 be Miocene, although these terms are not used by the author. The 

 memoir concludes with a description of the post-Siwalik or Grau- 

 getic formation, which is most distinctly separated from that of 

 the Siwalik Hills, without any approach to shading off or passing 

 from one into the other. 



The second memoir to which I have alluded, is on the geolo- 

 gical structure of parts of the districts of Salem, Trichinopoly, 

 Tanjore, and South Arcot in the Madras Presidency (being the 

 area included in Sheet 79 of the Indian Atlas, by Messrs. King and 

 Foote of the Geological Survey of India). One of the most re- 

 markable features in this district are the beds of magnetic iron- 

 ore which occur amidst the metamorphic gneiss-rocks, and the 

 supply of which seems to be practically inexhaustible. They are, 

 moreover, of great interest and value to the geologist, as they, 

 more than any of the other strata, enable him to decipher the great 

 contortions and flexures which have tended in great measure to 

 produce the existing form of the surface in these regions. 



Two classes of rocks, of igneous or quasi-igneous origin, are also 

 represented in this region, namely, trap-rocks and granites. The 

 latter is principally developed in the Trichinopoly district, where it 

 forms a band of considerable extent, and from four to six miles 

 wide, apparently intruded between the planes of bedding of the 

 gneiss. But there appear to have been, at least, three periods of 

 intrusion of granite into the rocks which now constitute the gneissic 

 series, two of which are probably much older than the third. 



The superficial deposits and soils are next described, consisting 

 of Laterite, Cotton soil, and Kunkur. With the exception of a 

 few fossils, as a cast of a Terebratula, a species of Lithophagus, 

 a Coral, and a Cidaris, found in the Cuddalore Sandstones, which 

 are considered to be post-cretaceous, fossils do not appear to 

 be abundant in this district. The laterite is generally found on 

 the top of the grit series. It is a brown ferruginous deposit, and 

 occurs in two forms in the district, as a regular aqueous deposit 

 of great extent, or as the effects of decomposition in situ of highly 

 ferruginous rocks. In the latter form it is called Lithomarge, 

 and it is essentially a decomposed gneiss in situ. The true laterite 

 consists of an agglomeration of small rounded particles cemented 

 together by a ferruginous sandy clay, the nodules consisting of 

 the same ferruginous sandy clay, with a concretionary structure. 

 The Kunkur is a greyish-white calcareous deposit, similar in struc- 

 ture to the laterite, and occurring as little grains or concretions. 

 It is also either the result of deposition from water, or of the de- 

 composition of rocks in situ. 



The general results of the Novara Expedition, undertaken by 



