474 Reviews — Geology in Northern Assam. 



are nearly always in the state of casts, the moulds of which retain 

 quite sharply the impression of the ornaments of the shell surface, 

 much the same as in the case of the English fossils from the Chalk 

 Rock. M. Vincent describes the MoUusca, M. Dollo Podocnemis 

 eongole7isis^ and M. Leriche some new fishes, Hypolophites mayombensis, 

 Mijliolatis dispar, and a couple of Agassizian species of Lamna and 

 Odontaspis. Leriche also gives a sketch of the Eocene fish fauna of 

 the west coast of Africa, which confirms the opinion that the general 

 fauna is of early Eocene age. The papers are well illustrated. 



IX. — Geological Explorations in Northern Assam. 



The Records of the Geological Survey of India, vol. xlii, pt. iv, 

 1912, contains accounts of two traverses made by geologists 

 accompanying punitive expeditions against the hill tribes of Northern 

 Assam. 



E. H. Pascoe, M. A., gives an account and sketch map of "A Traverse 

 across the Naga Hills of Assam from Dimapur to the neighbourhood 

 of Sarameti Peak". The traverse is joined up with earlier mapping 

 by Hayden further to the north. Near Dimapur the Tertiaries are 

 represented by the Tipam sandstones. These are bounded on the 

 east by a reversed fault, bringing in the sandstones and carbonaceous 

 shales of the Disang Series. There is a band of serpentine, derived 

 from gabbro and peridotite intrusions probably of pre- Disang age. 

 The Chimi conglomerate forms an important horizon as it separates 

 the Disang Beds to the west from the Makwari Beds to the east ; 

 these latter differ from the Disang Series only in the degree of their 

 metamorphism, which increases eastwards. Blue slates of good 

 roofing quality occur in the Tepe and Tuzu Rivers. The entire 

 absence of limestone between the Tipam Beds and Sarameti Peak 

 is notable. Correlation with other areas is difficult ; provisionally 

 the Disang Series is correlated with the Negrais, and the Makwaris 

 with the ' Axials ' of Burma. 



J. Coggin Brown, M.Sc, accompanied the Abor Expedition of 

 1911-12. The geological results of this expedition are given in 

 "A Geological Reconnaissance through the Dihong Valley ". This 

 was practically untouched ground, and the traverse adds considerably 

 to our knowledge of the mountains bordering Upper Assam. After 

 leaving the alluvial deposits near the mouth of the river, the road 

 crosses Pleistocene gravels resting on Siwalik sandstones containing 

 fragments of lignite. These Tertiary beds are succeeded by 

 carbonaceous shales and quartzites of Gondwana age, associated with 

 a large series of basalts — the Abor Volcanic Series. The junction 

 between Siwalik beds and Gondwanas is probably an overthrust. 

 Above the Gondwanas the route traverses a large series of slates, 

 phyllites, and dolomites, comparable with the Daling and Baxa Beds 

 of the Darjeeling area. These are followed by true mica-schists. 

 There is frequent repetition of similar groups of rocks, which is due 

 to the existence of closely-packed sinuous folds, often overfolded, 

 and having a general N.E. and S.W. trend. Little of economic value 

 was found, the coal being too inaccessible to pay for the working. 



