The lowest rocks belong to the great trappean region of the rap. Dakhan, which is roughly estimated to cover an area of 200,000 square miles. They consist of a series of basaltic flows, all nearly horizontal or presenting the appearance of having been so originally. In some parts of the Western Ghats their vertical thickness is from 4,000 to 5,000 feet, and probably where thickest they may amount to 6,000 feet and more; but this is the thick end of the formation, and the flows thin out towards the extremities in a series of broad ledges or steps. The rocks are believed to have been formed between the highest Mesozoic and the lowest Cainozoic periods, or between the Upper Cretaceous and the Lower Eocene formations. They are divided into three groups:—

1st.— The tipper traps and inter-trappeans of Bombay, 1,500 feet thick.

2nd.—The middle traps, to which those found in this district belong, 4,000 feet thick.

3rd.—The lower traps and inter-trappeans of Nagpur, and the Mekalgandi Pass, &c., towards the limits of the formation, 500 feet thick.

From the fact that the inter-trappeans of the lowest and highest groups are fresh-water sedimentary rocks, and also from the frequent occurrence of volcanic breccia in the highest and middle group, it has been inferred that the trap rocks of the Dakhan are of sub-aerial origin. No remains of extinct volcanoes have been discovered, from whence this great mass of volcanic matter could have been ejected. Large numbers of dikes are found on the Western Coast, but there are very few in this district, and the only place that has the appearance of a crater—at Lonar in Berav, adjoining the district to the east of Jalna—is remarkable for the absence of dikes in the vicinity. It is however clear from the occurrence of inter-trappeans, that the rocks were not all thrown up in one continuous flow; but that there were long intervals of repose, during which time lakes were formed, and different conditions of life existed, which were subsequently enveloped during periods of activity. This mode of occurrence gives a peculiar aspect of stratification appertaining to the sedimentary rocks, and terraces rise upon terraces, continuous over great distances, as if indicating the different flows in their order of succession. Yet in a class of rocks which present much uniformity, and which insensibly graduate into one another, it is not easy to draw the line between each succeeding flow. Nor are their degrees of compactness a sufficient index of their order, as this might be due as much to their chemical composition, and the circumstances under which they were discharged over the surrounding surface, as to their order of superposition. Thus several succeeding flows are crystalline in character, while others are amygdaloidal and vesicular. Still a thin parting of clay more or less indurated might form a kind of dividing line; the upper lavas may be more vesicular or more amygdaloidal, and the lower more basaltic; while perhaps the lowest amygdaloidal flows, next to the point of junction, may contain little tubular penetrations subsequently filled in by infiltration, indicating the rise of gases from the surface beneath. The lines of demarcation however, will be faint or sharp, just as the periods of repose are short or long; so that it is not unlikely that when two beds of similar appearance and composition occur together, they may be confounded as one. The different flows are of no great thickness, and many of the more amygdaloidal beds appear to be made up of several smaller flows from six to ten feet each, while the crystalline flows are perhaps about fifteen feet each.