3 
, 
. 
; 
; 
: 
American ie aes by T. S. Hunt. 393 
in a separate form, with some cia would we think be most 
acceptable to the scientific pu 
he other work before us is Prof H. D. Rogers’ elaborate re- 
port on the geology of Pennsylvania, giving the results of the 
Survey of that State for many years carried on under his direc- 
tion, and embracing a minute description of those grand exhibi- 
tions of structural geolog Bin oe have rendered that State elas- 
sic ground for the st udent. volumes are copiously illustra- 
ted with maps, dechicnts and fgectes of organic remains, and the 
admirable studies on the coal fields of Pennsylvania and Great 
Britain add much to its value. 
The oldest series of rocks known in America is that whick 
has been investigated by the officers of the Geological Survey of 
pena he nd by them designated the Laurentian system. It is 
now several years since we suggested that these rocks are the 
stytibvadeian of the oldest crystalline strata of western Scotland 
and Senge * This identity has since been established —_ 
Sir R. I. Murchison in his late remarkable researches in 
northwestern Highlands, and he has adopted the name of is 
Laurentian system for these ancient rocks of Ross, Sutherland, 
and the Western Islands, which he at first called ‘fundamental 
gneiss. These are undoubtedly the oldest known strata of a 
earth’s crust, and therefore offer peculiar interest to the geol 
As displayed i in the Laurentide and Adirondack mountains, t oy 
exhibit a volume which has been estimated by Sir William Lo- 
gan to be nee to the whole palzozoic series of North America 
In its greatest development. The Laurentian series consists of 
gneiss, generally granitoid, with great beds of quartzite, some- 
times conglomerate, and three or more limestone formations, (one 
» 
mba: . Intheu 
extensiee’ formation of ooke consisting chiefly of basic feldspars 
without quartz and with more or less oxene, is met 
The peculiar characters of these latter strata, not less than the 
absence of argillites and talcose and chloritic schists, conjoined 
with various other mineralogical characteristics seem to distin- 
guish the Laurentian series throughout its whole veamedie so far 
as yet studied, from any other system of ¢ It 
sse Géologique du Canada, 1855, p. 2 1. 
t beh Saeed Ged. Society, vol. xv, 353; xv, 215. 
