Before commencing the study of the stratigraphical geology of India, it is necessary to acquire some knowledge of the principal physical features. The student should make himself familiar with the main aspects of its geography, the broad facts regarding its external relief or contours, its mountain-systems, plateaus and plains, its drainage-courses, its glaciers, volcanoes, etc. This study, with the help of physical or geographical maps, is indispensable. Such a foundation-knowledge of the physical facts of the country will not only be of much interest in itself, but the student will soon find that the physiography of India is in many respects correlated to, and is, indeed, an expression of, its geological structure and history.
The most sahent fact with regard to both the physiography Geological and geology of the Indian region is that it is composed of three distinct units or earth-features, which are as unlike in their physical as in their geological characters. The first two of these three divisions of India have a fundamental basis, and the distinctive characters of each, as we shall see in the following pages, were impressed upon it from a very early period of its geological history, since which date each area has pursued its own career independently. These three divisions are:
1. The triangular plateau of the Peninsula, with the island of Ceylon.
2. The mountainous region which borders India to the west, north, and east, including the countries of Afghanistan, Baluchistan, and the hill-tracts of Burma, known as the extra-Peninsula.