198 



LYELL'S ELEMENTS OF GEOLOGY. 



Different character of Chalk in South of Europe. 



formation, although still exhibiting some of the same mineralo- 

 gical peculiarities, is nevertheless greatly changed. Its calca- 

 reous division consists for the most part of compact crystalline 

 marble, often full of nummulites (see Fig. 180.), and those por- 



Fig. 180. 



Nummulite limestone ; Peyrehorade, Pyrenees. 



a External surface of one of the nummulites, of which longitudinal sections are 



seen in the limestone. 

 b Transverse section of same. % 



tions which may be imagined to represent the green-sand, are 

 composed of shales, grits, and micaceous sand-stone, containing 

 impressions of marine plants, together with lignite and coal. 

 There are also beds of red sandstone and conglomerate, belong- 

 ing to the same group. These rocks ascend gradually into the 

 highest part of the Pyrenees, and cross over into Spain, where 

 the cretaceous system assumes a character still more unlike that 

 of northern Europe. 



Here, as on the north side of the Pyrenees, the most conspicu- 

 ous fossils are .hippurites, sphaBrulites, and nummulites. The 

 last-mentioned fossil, so called from its resemblance to a piece 

 of money, is a genus of mollusca, very abundant in the tertiary 

 strata of Northern Europe ; but only met with in chalk in the 

 South of Europe. 



So many species and genera of shells now wanting in our 

 northern seas, are frequent in the Mediterranean, that we need 

 not be surprised, when following from north to south the deposits 

 of the old cretaceous sea, at finding similar modifications in or- 

 ganic forms. 



The cretaceous rocks in the Alps, Italy, Greece, and Asia 

 Minor, are distinct in like manner from the type of that forma- 

 tion in the North of Europe ; yet their age in most of these 

 countries can be clearly ascertained, partly by following them 

 continuously from the north in the manner above described ; and 

 partly by their position below the tertiary, and above the oolitic 

 strata. 



