Revieivs — Geology of North- Eastern Rajputana. 175 



Indian Geology. 



II. — The Geology of North-Easteen Rajputana and Adjacent 

 Districts. By A. M. Heron, B.Sc, F.G.S., Assoc.Inst.C.E., 

 Assistant Superintendent, Geological Survey of India. Memoirs 

 of the Geological Survey of India, a'oI. xlv, pt. i. Calcutta, 

 1917. Price 4s. 



niHIS memoir deals with the re-survej" of the above district, which 

 X is roughly contained in a triangle, with the cities of Agra, Jaipur, 

 and Delhi at its apices; the original survey was carried out by C. T. 

 Hackettin 1881 and is now out of date. The region is one of old folded 

 rocks; these had been denuded to a peneplain, uplifted a second 

 time, and now are in an advanced stage of the second cycle of 

 denudation. The greater part of the district is covered with 

 alluvium, but in the south-west part the old rocks come to the 

 surface over a considerable area; the dips here are always high, and 

 the hard bands stand up as ridges with broad valleys between: this 

 close connexion between geological structure and topography is not 

 common in this part of India. 



Two distinct geological systems can be separated — an older, the 

 Aravalli system of Archaean age, which may be correlated with 

 the Dharwar system of Cental and Southern India, and a newer, the 

 Delhi system, wliich is placed among the Lower Purana rocks. The 

 interval separating the two systems corresponds to the Ep-archaean 

 interval of North America. 



The Aravalli rocks are exposed along the anticlines of the post- 

 Delhi folding and consist of highly metamorphosed sediments with 

 some intrusive granites, amphibolites, and quartz veins. Tlie Delhi 

 system begins with an inconstant quartzite which is overlain by the 

 llialo limestone. This limestone is a pure dolomite and usually 

 forms low-lying country, with the exception of a few residual knolls 

 of ironstone formed by metasomatic alteration. The succeeding 

 Alwar series consists of quartzites, grits, and associated volcanic 

 rocks, invaded by granites, pegmatites, and basic sills, now altered 

 to amphibolites. These rocks are succeeded by a banded siliceous 

 limestone, the Kushalgarh limestone, with which is associated a 

 peculiar rock known as the "hornstone breccia". Finally, the 

 Delhi system is completed by the Ajabgarh series, which is composed 

 chiefly of clays with impure quartzites and limestones, and shows 

 deeper-water conditions than the Alwar series. 



The hornstone bi'eccia which is found sometimes below and some- 

 times above the Xushalgarh limestone is a very remarkable rock. It 

 consists of angular fragments of quartzites, identical with the 

 Alwar and Ajabgarh quartzites, some pieces of slate similar to the 

 Ajabgarh slates, and brecciated white vein quartz in a very finely 

 granular matrix, the grains of which are coated with limonite, and 

 which is occasionally sufficiently ferruginous to be used as an iron 

 ore. It is suggested that the rock was formed by the crumpling of 

 alternating beds of quartzite and slate under the stress of the post- 

 Delhi folding; the quartzites, being brittle, would break and be 

 pushed into the more yielding slates. Into this shattered rock, 



