30 Feathtrstonhaugk s Geological Report. 



sensibly into serpentine, a rock which abounds in this country 

 in the region of the primordial rocks. 



The geological student, in entering the field of observation 

 in the United States, will find that the varieties of all the 

 formations which have been alluded to are very numerous, 

 and that they occasionally succeed each other in so irregular 

 a manner as to preclude the supposition that they have come 

 into their places in any determinate order of succession. 

 Regarding them theoretically as the products of igneous fusion, 

 the embarrassment is increased by perceiving some of them to 

 be un stratified, and others stratified. That the first may have 

 resulted from the cooling down of mineral matter when in a 

 state of igneous intumescence, is intelligible enough ; but that 

 contiguous rocks, having the same origin, and which form 

 perhaps the greater portion of the surface, should be disposed 

 in parallel strata, is not so easily explained. Yet, if any one 

 should be disposed to attribute to them the same aqueous 

 origin to which the sedimentary stratified rocks are referred, 

 he must remember not only that the mineral constituents of 

 those unstratified and stratified masses are the same, but that 

 most of them actually pass into each other by the absence or 

 presence of one or more of their mineral constituents. What 

 has been called the stratification of these ignigenous rocks, 

 may be owing to the principle which occasions their fissility, 

 such as the distribution of the plates of mica parallel to the 

 strata. It is evident, however, that the nature of the primor 

 dial rocks has yet to be carefully studied before we can, with 

 perfect satisfaction, believe this difference between them to 

 be due to modifying causes, and refer these two classes of 

 rocks to the same origin. 



Much of the irregularity with which they succeed to each 

 other is owing in some cases to the same mineral compound 

 being repeated in distant localities, and in others to slight 

 variations of that compound. Most of these ignigenous masses 

 appear in the character of intrusive bodies. Granite, the 



