JASPER. 547 



felspar or clay, occur in contact with granite, 

 they pass into jasper if the clay abounds ; while, 

 in other places, they are converted into chert if 

 less of that earth is present ; or, if pure, are ren- 

 dered perfectly crystalline. These examples are 

 to be found in Aberdeenshire, and are valuable 

 on account of the light which they throw on the 

 origin of this rock. 



In all the following situations, it must be re- 

 ferred to the secondary class, unless, in the follow^ 

 ing instance, as well as in that just quoted, it is 

 conceived to be a primary rock influenced by the 

 basalt in its vicinity. 



In this case, which occurs in France, accord- 

 ing to the authority of Soulavie, it occupies a 

 position intermediate between granite and basalt. 

 In the other instances in which it occurs in the 

 secondary class, it is always in some manner 

 connected with the overlying, or trap rocks. 



When the indurated claystones of this family, 

 assume strong and ornamental colours, they are 

 commonly known by this name, not perhaps 

 alwaj s very properly. But, in some cases, these 

 rocks, which, in most instances, pass by indura- 



N N 2 



