[ ,6 ] 



these strata do not occur in such regular succession exposed 

 to the surface, the same order can be traced all over the 

 surface of the earth. 



20. If we study the character of the rocks so exposed in 

 succession, either vertically in cuttings or horizontally as we 

 pass from field to field, and district to district, we will find 

 two classes of rocks, stratified and unstratified. Unstratified 

 rocks are igneous in origin, i.e., thrown up from the burning 

 bowels of the earth. The stratified rocks have been formed 

 by fluvial lacustrine or marine actions, sedimentation, strati- 

 fication under pressure and infiltration of substances acting 

 as mortar. Heat played an important part in the formation 

 of some sedimentary rocks. These are called metamorphic 

 rocks or schists. 



21. Studying the geological strata from below upwards, 

 we find the following order prevailing in the deposition of 

 these strata : 



The first, that is, the lowermost stratum, may be called 

 the Lower Magma. These are basic rocks rich in earthy bases 

 and oxides of iron. Volcanic action has exposed this deep 

 liquid layer to the surface of the earth in the form of Basalt, 

 Dolerite and Zeolite. Greenstones and basalts generally are 

 called trap rocks as they occur in the form of steps on hill 

 sides. The solidification of the Lower Magma taking place 

 after volcanic eruption on the surface of the earth, the Lower 

 Magma occur chiefly as volcanic rocks. These volcanic 

 eruptions did not take place in the earliest geological ages, 

 but later on. The first eruptions took place from the Upper 

 Magma, i.e. } the lighter siliceous or acidic layers. The ba- 

 salts are found chiefly in the meso-zoic and neozoic 

 formations of which we will speak later on. All over the 

 plains of Deccan occur trap rocks, usually in horizontal 

 layers of 6 to 90 feet, each layer being a separate lava deposit 

 evidencing a succession of volcanic eruptions. The total 

 depth of these successive deposits of trap reaches in some 



