6 VREDENBURG : RECENT ARTESIAN EXPERIMENTS JN INDIA. 



examples of the London or Paris basins, which are termed "basins 

 of disturbance" in contradistinction to " basins 



Basins of disturbance ..., • • ,. T t . 



and of original deposi- ot original deposition, He brought to notice 

 the fact that the structure favourable to artesian 

 action might be caused either by subsequent tilting of strata that 

 were originally horizontal, or else that the same action might take 

 place in undisturbed strata that have been deposited in an inclined 

 position, as in the case of the strata occupying alluvial plains. 

 Sedimentary rocks may be, for the purposes of the present case, 

 divided into two principal sections : there are, first, those ancient 

 rocks which form such a large proportion of the earth's crust, and 

 which geologists usually classify as palaeozoic, mesozoic (secondary) 

 and tertiary. These consist of alternating strata of varying thick- 

 ness, often remarkable for the small amount of variation which they 

 exhibit over considerable areas. They have usually been deposited 

 upon the floor of the sea at some distance from the coast, and their 

 distribution by marine agency has resulted in their great constancy 

 over wide areas. Owing to changes in the relative level of land 

 and sea, or to a bending or corrugation of the originally flat surface, 

 these strata have now come to constitute dry land and may even 

 rise into high mountains. It is the inclined position thus assumed 

 which often allows the formation of more or less water-tight reser- 

 voirs. The other class of strata are those that have been called 

 diluvial, quarternary, pleistocene, or post- tertiary, the two latter 

 terms being more commonly in use. They are newer than the 

 strata of the first category, and consequently they rest upon them 

 when both exist together in the same region. They merge insen- 

 sibly into the alluvial deposits whose formation continues over the 

 land at the present day. Like these recent deposits, they are 

 generally land formations instead of being of marine origin as in 

 the case of the majority of the older strata grouped in the first 

 category. They often occupy a considerable horizontal surface, 

 but they never attain the enormous thickness frequently exhibited 

 ( 6 ) 



