390 Proceedings of Philosophical Societies, [May, 



irifiing excess of the alkaline precipitant. In the cases of cobalt 

 and cerium, the alkahne carbonate may be added in considera- 

 ble excess without separating any of those metals, and their 

 solution so freed from iron is tlien a most delicate test of the pre- 

 sence of the latter metal. 



Apiil 12. — A paper was read. On the Mean Density of the 

 Earth, by Dr. C. Button. 



At the same meeting a paper was read, On the Restoration of 

 a Portion of the Urethra in the Perinaeum, by H. Earle, Esq. 



GEOLOGICAL SOCIETY. 



Feb. 16. — An introductory essay on the Geology of India, by 

 H. T. Colebrooke, Esq. MGS. was read. 



The physical geology of India may be considered as resolving 

 itself into three great divisions ; viz. 1 . The peninsular tract, 

 which constitutes the south of India ; 2. The belt of flat country 

 extending from sea to sea, and distinguished by the name of 

 Middle India; 3. The continental mountains which form the 

 northern limit of India, rising between the middle region and 

 the vast extent of Tartary, and extending more than 15° of lon- 

 gitude in a direction from WNW to ESE. 



In the champaign country constituting middle India, three 

 principal divisions may be noticed ; 1. The tract watered by the 

 Ganges and its tributary streams ; 2. A Tract watered by the Indus ; 

 and, 3. The intermediate desert, on which the Saraswate loses 

 itself. 



Of this country, a striking feature is the total absence of pebble 

 or rolled stones of any kind, except in the beds of the rivers, for 

 a few miles after they quit the hills ; and the subsoil of the plain 

 is every where earthy and comminuted, except in certain 

 instances, where nodules, or concretions, have been found. 



Throughout this extensive plain, there is neither mine nor 

 quarry : the banks of the river being usually precipitous on one 

 side, and shelving on the other, exhibit sections of strata down 

 to the level of their beds. Scarcely any other natural section is 

 found ; and the sinking of wells, or boring for water, is the only 

 opportunity which art presents for the examination of strata. 



The surface is every where alluvial, and the strata, as far as 

 they have been observed, are horizontal. Beneath the superfi- 

 cial mould the subsoil is sand, clay, or loam in layers more or 

 less intermixed, and distinguished by colour or texture. In the 

 inferior strata of clay, nodules or concretions of the same sub- 

 stance are sometimes met with. The upper strata of siliceous 

 sand, as well as that found in the bed of the Ganges, generally 

 abound in fragments of mica ; but in some places, beds of sand 

 contaminated with salt, and in others, beds exclusively composed 

 of salt, are found . 



In a very few spots, and at no great depth below the surface. 



