PRIMARY STRATIFIED ROCKS. 51 
agents ; by rains, torrents, and inundations ; at 
that time probably acting with intense violence, 
and washing down and spreading forth, in the 
form of mud and sand and gravel, upon the 
bottom of the then existing seas, the materials of 
primary stratified rocks, which, by subsequent 
exposure to various degrees of subterranean heat, 
became converted into beds of gneiss, and mica 
slate, and hornblende slate, and clay slate. In 
the detritus thus swept from the earliest lands 
into the most ancient seas, we view the com- 
mencement of that enormous series of derivative 
strata which, by long continued repetition of 
similar processes, have been accumulated to a 
thickness of many miles.* 
The total absence of organic remains through- 
* Mr. Conybeare (in his admirable Report on Geology to the 
British Association for the Advancement of Science, 1832, 
p. 367) shows, that many of the most important principles of 
the igneous theory, which has been almost demonstrated by 
modern discoveries, had been anticipated by the universal 
Leibnitz. " In the fourth section of his Protoggea, Leibnitz 
presents us with a masterly sketch of his general views, and, 
perhaps, even in the present day, it would be difficult to lay 
down more clearly the fundamental positions which must be 
necessarily common to every theory, attributing geological 
phenomena in great measure to central igneous agency. He 
attributes the primary and fundamental rocks to the refrigeration 
of the crust of this volcanic nucleus ; an assumption which well 
accords with the now almost universally admitted igneous origin 
of the fundamental granite, and with the structure of the primi- 
tive slates, for the insensible gradation of these formations ap- 
pears to prove that gneiss must have undergone in a greater, 
