EQUIVALENTS OF CHALK. 205 



ivitli Cornwall and Ireland, and lijf another joining 

 Scotland vdih Scandinavia. 



The above area includes the whole of the white chalk ; 

 but when we trace this chalk southwards into Bohemia 

 and Saxony we find that it has undergone a very 

 remarkable change. Thus, although it contains the same 

 fossils as to the northward, the rock itself, instead of being 

 the pure white limestone to which we have been accustomed, 

 consists of a series of massive sandstone about as unlike 

 chalk as anything well could be. It is probable, indeed, 

 that these cretaceous sandstones, as we may call them, 

 were formed in a gulf on the southern coast of the white 

 chalk sea, which was unfavourable to the deposition of 

 chalk itself ; and as these sandstones were undoubtedly 

 deposited at the same time a.s the ]3ure chalk, we thereby 

 learn the very imjjortant geological lesson that similarity 

 or dissimilarity in the mineralogical structure of a rock is 

 a matter of very minor import indeed. We may illustrate 

 this by reference to architecture. Thus, a Gothic church 

 may be built either of sandstone, limestone, marble, or, 

 for the matter of that, Ijrick ; but it will still be (exclusive 

 of course of our so-called modern Gothic) absolutely 

 characteristic of one particular period of European archi- 

 tecture. This Gothic style will be distinguished by certain 

 peculiarities in the structure of its arches and pillars, as 

 well as by the ornaments with which they are embellished. 

 Just so in geology we have a chalk or cretaceous style, in 

 which, although the rock itself luay be either chalk or 

 sandstone, or limestone, or slate, yet its architectural 

 details — that is to say, its fossils — will be the same, not 

 only throughout Europe, liut within certain limitations of 

 variation, over the wh(jle world. This is one of the 

 important lessons to be learnt by a comjjrehensive study of 

 our white chalk. 



The second great lesson taught by the white chalk is, 

 however, of perhaps still more importance. We have seen 

 that the white chalk was deposited in a sea cut oif from 

 free communication with the Atlantic to the west and 

 north ; and the range of the Ardennes which formed its 

 shore in the south-west, together with the evidence of the 



