I'lnsKAl, II isi(»i;\- S.") 



leiice ot'carbonaceoiKs and calcareous material (particular!}' in the Niscon- 

 litli) appears to indicate the iibundant presence oforganisnis of some kind 

 at this time. 



Although no evidence has been found of any great physical break, 

 the conditions indicated by the Ufjper half of the Cambrian are very dif- 

 ferent from those of the lower. Volcanic materials, due to local eruptions, 

 were accumulated in great mass in the region bordering on the Archean 

 axis to the west, while on the east materials of this kind a})})ear to l)e 

 mingled with the preponderant shore deposits of that side of the Archean 

 land, and to enter sparingly into the composition of the generally calca- 

 reous sediments lying still farther eastward. Where these sediments 

 now appear in the eastern part of the Laramide range they are chiefly 

 limestone, indicating marine deposition at a considerable distance from 

 any land. 



The histor}' of the Ordovician, Silurian, and Devonian times is very 

 imperfectly known. Marine conditions still prevailed to the eastward 

 of the Archean axis and were probably continuous there, but our knowl- 

 edge of the region to the west, while as yet almost entirely negative in 

 its character, is not sufRciently complete to enable us to assume the ex- 

 istence of any extensive land area in that quarter. In the Devonian the 

 sea is known to have covered a great area in the interior of the continent, 

 extending far to the north in the Mackenzie basin, and it appears prob- 

 able that considerable portions of the western part of the Cordilleran 

 region were also submerged, particularly to the north. 



About the beginning of the Carboniferous period and thence onward 

 the evidence becomes much more satisfactory and complete. In the 

 earlier part of the Carboniferous, marine sediments, chiefl}'' limestones, 

 were laid down everywhere to the east of the Archean axis, while to the 

 west of that axis (which was i)robably in large part itself submerged) 

 ordinary clastic deposits, mingled with contemporaneous volcanic ma- 

 terials, were formed, tranquil epochs being marked by the intercalation 

 of occasional limestone beds. It is not clearly apparent from what land 

 the clastic materials were derived, but the area of vulcanism at this time 

 was very great, covering the entire western part of British Columbia to 

 the edge of the continental plateau and, as now known, extending north- 

 westward into Alaska and southward to California. 



In the later time of the Carboniferous, however, the volcanic forces 

 declined in their activity, and a great thickness of calcareous marine de- 

 posits occurred with little interruption of any kind. The area of land 

 to the eastward was probably increased, for there is souje evidence to 

 show a first gentle uprising in the Laramide region at this time (or at 

 least a cessation of subsidence), and no late Carboniferous strata have 

 so far been found there. 



