GREEN SAND GAULT. 



71 



and yellowish sands, which are frequently ferru'ginous, containing 

 masses of limestone, clays, and sandstones of more or less com- 

 pactness : it also comprises the quadersandstein and plsener-kalk 

 of German geologists. 



11. Gault is si stiff clay of a blue colour, and the inferior por- 

 tion of it in England abounds in iron py'rites, while the uppe-r part 

 contains green particles of the si'licate of iron. Various nodulea 

 and concretions are found throughout, which are sometimes fossili'- 

 ferous, but more frequently obscure and of doubtful origin. Gault 

 is a provincial term, used originally in the middle of England to 

 designate the brick-clay, which there belongs to the creta'ceous 

 system. 



12. Above the green sand formation, the calcareous .part be- 

 comes more abundant ; at first it is mixed with sandstone, and then, 

 little by little, becomes isolated, and now contains only green parti- 

 cles of si'licate of iron, which, from being at first very abundant, 

 gradually disappear : this is the chloritic chalk, which is some- 

 times friable, and at others solid. The green particles having 

 totally disappeared, the limestone is found alone, sometimes in form 

 of pure chalk, of more or less solidity, and occasionally becomes 

 very compact ; here we have argilla'ceous or arena'ceous limestone, 

 and finally sands, or nearly pure sandstone. From these result the 

 chalk marl, or representatives of it. 



13. Organic remains 



are 



in 



very abundant 

 these deposits, and in 

 species and even in ge- 

 nera are very distinct 

 from those of the preced- 

 ing formations. Immedi- 

 ately above the wealden 

 is a marly bed, charac- 

 terized by the presence 

 of a species of Ex'ogy' 

 ra (/?>. 125) five or 

 six inches in diameter, 

 not known in the neo- 

 comian. According to 

 M . Leymerie, the nu'- 

 cula peclina'ta (Jig. 

 126) is a characteristic 



Fig. 125. Ex'ogy ra sinua'ta. 



shell of the gault or blue marl. Belonging to the green sand 



11. What is gault ? What is the origin of the name ? 



12. What succeeds the green sand formation? What is chloritic chads ^ 

 What is chalk marl ? 



13. What organic remains are found in these deposits ? 



27* 



