Featherstonhaugh^s Geological Report. 31 



lowest rock in the series, is found in a modified form overly- 

 ing fossiliferous strata in the Alps. Serpentine, which is but 

 a modification of hornblende matter, overlies sedimentary 

 limestone in extensive tracts of the Appenines, and trap 

 rocks, of which modern lavas are but modifications, are found 

 injected into almost every formation, from the granite up to 

 the surface ; indeed, in the extinct volcanoes of Auvergne, the 

 ancient lavas have been clearly projected from beneath the 

 granite. 



There is another important rock, clay slate, not inserted in 

 the tabular view, which is thought to pass gradually into some 

 of the schistose primordial masses with which it is associated ; 

 yet it is a stratified body, and in its mineral structure is some- 

 times hardly distinguishable from the roofing slates, which 

 are enumerated amongst the sedimentary deposites of what 

 have been called the transition beds. 



These observations on the formations of the inferior divi- 

 sion are offered not only for the assistance of the geological 

 student, but in some degree to incite the able mineralogists 

 of this country who reside in the regions of the primordial 

 rocks, to make a precise and analytic study of their mineral 

 structure and constituent affinity with each other, and to note 

 all the circumstances attending the order in which they are 

 seen to succeed and overlie each other. Repeated observa- 

 tions made in various parts of the Atlantic frontier, will pro- 

 duce a great deal of valuable information. By such means 

 alone, we shall be able to compare the natural order and con- 

 stituency of the primordial rocks of the United States with 

 those which prevail in distant countries ; and thus, in time, a 

 unity of intellect may be directed to the development of the 

 most ancient parts of the structure of the accessible portions 

 of the earth, and of some principles connected with the min- 

 eral and metallic bodies, that cannot fail to be valuable in an 

 economical point of view. 



