346 The American Geologist. December, 1898 
exposed upon the North American continent. J soon found, however, that 
the time at my disposal would make this impracticable, and I decided 
to take up the history of the deposits that accumulated in Paleozoic 
time on the western side of our continent, in an area that, for conven- 
ience, I shall call the Cordilleran sea.* This was chosen as (1) I was 
personally acquainted with many of its typical sections; (2) there was a 
broad and almost uninterrupted sedimentation during Paleozoic time, 
and (3) there is a prospect for obtaining more satisfactory data as a basi& 
of calculation, since calcareous deposits are in excess of those of me- 
chanical origin. 
We will now consider certain points in relation to the growth or evo- 
lution of the North American continent, as the deposition of mechan- 
ical sediments depends to a considerable extent on the character of the 
adjoining land area, and chemical sedimentation is also influenced by it. 
Growth of the Continent. 
The Algonkian sediments were deposited in interior and bordering 
seas that rilled the depressions and extended over the margins of the 
Archean continent. From the great thickness of mechanical sediments 
it was evidently a period of elevated land and rapid denudation. With 
the close of Algonkian time extensive orographic movements occurred 
that outlined the subsequent development of the continent. The lines 
of the Rocky mountain and Appalachian ranges were emphasized and 
the great basins of sedimentation west of them defined. Subsequent 
movements have elevated the old and formed new sub-parallel ranges. 
These movements were often of long duration and also separated by 
great intervals of time, as is shown by the long continued base levels of 
erosion during which the great thickness of calcareous deposits accu- 
mulated in the Cordilleran and Appalachian seas. Since Algonkian 
time the growth of the continent has been by the deposition of sedi- 
ments in the bordering oceans and interior seas and lakes within the 
limits of the continental plateau: and it is considered that the relative 
position of the continental plateau and the deep sea have not materially 
changed during that period. How much the deposits on the continen- 
tal border have increased its area is unknown, as at present they are 
largely concealed beneath the waters of the ocean. During Paleozoic 
time the two areas of greatest known accumulation were the Appa- 
lachian and Cordilleran seas, where .30,000 feet or more of sediments 
were deposited. In the Cordilleran sea sedimentation was practically 
uninterrupted (except during a short interval in middle Ordovician 
time) until towards the close of Paleozoic time. In the northern 
Appalacian sea it continued without any marked unconformity, from 
early Cambrian to the close of Ordovician time, and, south of New 
York, with relatively little interruption, until the clo6eof Paleozoic time. 
Certain minor disturbances occurred along the eastern border of the 
sea, but they were not of sufficient extent to affect a general conclusion, 
which is that the depression of the areas of deposition within the 
*See page :i~>7. 
