732 



GEOLOGY. 



Chalk. 



Gault. 



Green sand. 



invaded by igneous rocks, at Weinbohla on the Danube, and in the Pyrenees, by 

 granitic varieties. 



The members of the cretaceous system, and the order of succession in the strata, are as 

 follows : 



{Upper chalk a white and soft mass, with chert nodules at regular intervals, and layers of 

 flints. 

 Lower chalk a harder and variously tinted mass, either without or with fewer flints. 

 Chalk marl highly calcareous, bluish, laminated beds of clay. 

 Upper green sand a mass of sands, occasionally indurated to chalky or cherty sandstone, 



of green, grey, or white colour, with nodules of chert. 

 Soft bluish marly clay, with green grains, Tetsworth clay, Folkestone clay. 

 Lower green sand a considerable mass of green or ferruginous sands, with layers of 

 chert, local beds of gault, rocks of cherty or chalky limestone, and deposits of ochre and 

 fuller's earth. 



This is a detail of the system as it occurs in the south of England. In other cretaceous 

 localities some of the preceding beds are wanting. The north of England has no upper 

 green sand, Yorkshire none of the lower, which is largely developed in Lincolnshire. 

 The Carpathian Mountains have no chalk, but green sand in abundance ; and this is the 

 case also with the Alps. 



Green sand. This deposit, the base of the cretaceous system, divided into upper and 

 lower beds, separated by a seam of soft blue clay, derives its name from its arenaceous 

 composition and green hues, though yellow tints are frequently exhibited. The sand 

 presents various degrees of fineness, and is employed as a manure in some parts of the 

 United States with considerable success. The colouring matter has been analysed with 

 much care by several distinguished chemists, with the following results : 



If the fertilising power of the sand depended alone upon the potassa, the English and 

 Massachusetts deposits would obviously be of no value, but to its virtue as a manure the 

 oxide of iron and the other ingredients may contribute. The green sand contains nume 

 rous fossils, zoophytes, sponges, echinites, and shells, which appear in the terrain neoco- 

 mien of the French geologists, a deposit appertaining to the same formation. It has thus 

 been styled from the site where it is largely developed, in the neighbourhood of Neuf- 



chatel in Switzerland, an 

 ciently called Neocomium, 

 occurring also in the north 

 of France, in the south 

 west within the range of 

 the Pyrenees, and in Dau- 

 phiny and Provence. The 

 more remarkable shells 

 are, several species of 

 Trigonia, three-cornered, 

 Trigonia aiojformii. alluding to the shape, 



