Geology and Mineralogy. 171 
A third group, nonconformable with the earliest aplitic series, 
the relations with the intermediate mica-gneiss series being un- 
known, consists of mica and hornblende schists passing upward 
into slates, quartzites, limestones, and dolom 
Upon grounds set forth in Section IV of apie: I it is clear 
that the general Se Pet 9 prior to the deposition of the earliest 
Cambrian rocks wa — of a great mountain system, displaying 
lofty ranges made of ¢ rumpled strata, enormous Dponprceare a result 
of mechanical dislocation, and, finally, a type of hig untain 
sculpture of such broa ‘smooth forms as to warrant the belief 
that subaérial erosion had never carved and furrowed the mount- 
ain flanks with the sharp ravines characteristic of modern mount- 
ain topography. East of the Rocky Mountains, in the geological 
province of the Great Plains, there are no Archean outcrops; and 
when we consider the comparative thinness of Ae later sedimen- 
tary beds superposed over that region, the absence of outcropping 
Archean masses pies through Pe ‘latter sediments is excellent 
proof that over that area Archean mountain ranges did not exist. 
This is important as defiving the Archean Cordilleras within the 
limits of the modern Cordilleras, or, as is a more — correct 
view, the Archxan Cordilleras have determined no only the gen- 
eral area but much of the local deadlal a structure "of the modern 
Conair 
rounding and abutting against permanent Archean islands, which, 
ee the whole Palxozoic and Mesozoic, were ifted above the 
longitnde 117° 30’, where, from the evidences “of enseeraleseoe 
and the non-continuation of the beds westward, we are warranted 
in assuming the Paleozoic coast. * 
iewed regardless of the age of oh individual beds, the Palx- 
= series = be divided by the character of their materials 
o four great groups. The first is a purely detrital Cambrian, 
which, cs of comparatively fine sediments, in the presence 
of oceasional conglomerates gives evidence of repeated subsidence, 
