48 



OUTLINES OF GEOLOGY. 



108. The chalk formation occupies a considerable portion 

 of the surface of Europe. It preponderates in the South of 

 England and North of France, and the basins of London, 

 Paris, and the Isle of Wight, rest upon it. From France this 

 formation extends through Belgium into the North of Ger- 

 many, and thence through Poland into Russia, where it has 

 been traced as far as the Don. Chalk also occupies the 

 South of Sweden, and it appears probable that all the locali- 

 ties we have yet mentioned, form a single basin, on which 

 the modern and superior formations of the shores of the Bal- 

 tic rest. A distinct chalk formation exists in the North of 

 Ireland, another in Italy, and a third in Spain. Detached 

 formations are found at high levels among the Alps, and on 

 the Pyrenees, rising to 9000 feet. 



With this exception, the chalk is rarely found at elevations 

 of more than 600 feet. 



Chalk is unknown in the United States. 



109 The green sand group may be divided into four dis- 

 tinct formations : — 



(1.) Green Sand. This owes its colour to a chloritous 

 silicate of iron ; it contains, imbedded, much pyrites, but is 

 poor in other minerals. It is interspersed with beds of lig- 

 nite, in which is found a substance analogous to amber. 



(2.) A Plastic Clay, containing no carbonate of lime. 

 This is called Weald clay by the English, and is infusible in 

 a kiln. It contains no fossils, except fresh water shells. 

 The imbedded minerals are, cale-spar, selenite, and pyrites. 



(3.) Iron Sand. This is either sand stone, or conglome- 

 rate, cemented by oxide of iron. It lies in beds alternating 

 with loam, clay, marl, and fuller's earth. Its mineral con- 

 tents also lie in seams, and are hydrated oxide of iron, fossil 

 wood, and brown coal. 



(4.) Anargillaceous Carbonate of Lime, called Purbeck 

 marble by the English. . 



