GEOLOGY of India has been summarized, during the 19th century, by Mr. James Calder, Captain Newbold of the Madras arniy, Surgeon Carter of the Bombay army ; and lastly, and in the highest sense, in a joint work by Messrs. H. B. Medllcott, M.A., and W. T. Blanford, F.R.S. Its most striking feature is the difference between the rocks of the Peninsula proper and those of the countries lying beyond the great Intio-Gangetic alluvial plain. The investigations of Dr. Hugh Falconer have shown that, at a period geologically recent, the present Peninsula of India was a trian gular island, bounded on each side by the E. and W. Ghats, converging to Cape Comorin, while the base of the triangle was formed by the Vindhya mountain range, from which an irregular spur, forming the Aravalli mountains, extended north wards ; while between the northern shore of this island and a billy country, which isnow the Hima laya mountains, ran a narrow ocean strait. The .bed of this strait bccaine -covered with debris from the adjacent Himalaya on its northern shore, and with this debris became entombed and pre served many and various animal remains. The present condition of the country in Northern India has been produced by a subsequent upheaval of the laud, so that what was the ocean strait forms the northern plains of India, the long, nearly level valleys in which flow the Gauges and the Indus. Besides this, a great upheavement along the lino of the Himalaya has elevated a narrow belt of the plains into the Siwalik Hills (determined to be of tertiary age), and added many thousand feet to tho height of the Himalaya ; and facts tend to the conclusion that India had one long term and one protracted fauna, which lived through a period corresponding to several terms of the tertiary periods of Europe.
The rocks of the Peninsula, though for the most part of very ancient date, are far less dis turbed than those of the IIimalaya, Afghanistan, and Burma, many of them, like the Vindhyan sand stones, being still quite horizontal. All the evi dence goes to show that from a very early period in the history of the world, the greater part of the Indian Peninsula has been dry land ; whereas for many ages the Himalayan area was occupied by the sea, and the rocks of that region have been, down to very recent thne.s, and probably still are, subject to violent crushing and contortion. In fact, the arrangement of the strata shows that, notwithstanding the great outpourings of volcanic rock which constitute the Dekhan trap, the Indian Peninsula Ints from the earliest ages been one of the steadiest aud most fixed portions of the earth's crust, whilst the Himalayan area has been subject to violent oscillations of level ; and the highest mountains in the world probably owe their height to the circumstance that the elevating forces are still in operation.
The oldest rock known to occur in India is the gneiss of Bundelkhand. It is exposed over a roughly triangular area, lying between Kirwee, Gwalior, and the southern part of the Lalitpur district. Along its northern edge it is covered by the Gangetic alluvium, and on the other sides I it is bounded by a steep scarp of Vindhyan sand- I stones, or by a series of sub-metamorphic rocks I underlying the Vindhyan. Two other areas of gneiss occur in the Peninsula, but from their relations to the sub-metamorphic series, they are supposed to be of an age posterior to the gneiss of Bundelkhand. One of these extends, with hardly an interruption, from the Ganges in the neighbourhood of Bhagulpur, to Cape Comorin, and from the coasts of Madras and Orissa to Vin gorla and Nemaur, where it is covered by the Dekhan trap. The other occupies the central and southern part of the Aravalli Hills in Rajputana, and it may be continuous with the eastern gueiss of the Nerbadda valley, underneath the trap. An outlier of the &AMC kind of gneiss occurs in Assam. The gniess of Bundellthand is of remarkably simple and uniform composition, while that of the south and east of the Peninsula is much more complex, aud contains many extraneous minerals, among which may be mentioned the gold of the Wynad, and the immense deposits of magnetic iron ore that occur in many parts of the country. Resting upon the Bundelkhand gneiss, but more or less disturbed where in contact with the other gneiss of more recent age, is a series of partially meta morphosed strata of no great thickness, called the Bijawars, in Bundelkhaud. This group of strata can be traced on the outskirta of the gneiss, from Silang in Asaarn to the Nerbadda valley. Similar rocks flank the Aravalli Hills ; and detached out liers occur through Northern Itajputana and the S.W. Panjab, as far as the Korana Hills, beyond the Sutlej and Ravi, and within a few miles of the Panjab Salt Range. An upper aeries of trturition rocks can be traced near Gwalior, and in parts of the Madras Presidency.