Current Action in the Ordocicidn. — Raedeinann . 389 
stone over the wliole breadth of the continent, seeks an ex- 
planation in the theory, that, " the currents of tlie ocean 
which ordiiiarily swept over the land (the Labrador current 
from the north, along the eastern border, and the Gulf stream 
from the south, over the interior), must have had their action 
partly suspended." This view not only includes the assump- 
tion that current-action terminated the Trenton epoch, but it 
suggests also that the current observed in the Utica shale of 
the Mohawk region was part of the Labrador current. It 
came from north but under the influence of the diurnal rota- 
tion had a tendency to deviate in a westerly direction on ac- 
count of which tendency it pressed toward the east border of 
the then-existing land, crossed the region of comparatively 
shallow waters, which is supposed to have foreshadowed, dur- 
ing the Ordovician era, those ranges which arose at the end of 
that era — namelj^ the Green mountains and parts of the Ap- 
palachian system — and entered the continental basin in east- 
ern New York as a W. S. W. current. Dana says regarding 
this shallow region (op. cit. p. 211) : ''Along its course, there 
were Archjean islands and reefs, when the Silurian era 
opened,— ^portions of the Blue Ridge to the south, the High- 
lands of New Jersey and Orange and Putnam counties, N. Y., 
and the patches of Archaean rocks in New England being 
some of these areas. It was hence a barrier region to the con- 
tinent, over which the Atlantic currents flowed and waves 
broke ; and here, therefore, fragmental rocks — rocks of sand, 
pebbles, mud and clay — ought to have abounded." Investi- 
gations of the present currents have shown, that, on account 
of the increased velocity in the straits of an archipelago, the 
finer partly suspended silt, such as evidently formed most of 
the Utica shale, is carried farther away', while in the straits 
themselves, former deposits may be swept otf the floor of the 
sea. The Gulf stream has been found not to drop any de- 
posits in its direct course in the strait of Florida, while its 
lower part from the exit at Florida, where the current rapid- 
ly decreases in velocity, to cape Hatteras has been compared 
to a muddy river. Places where " hard bottom " has been met 
with on account of the scouring action of the currents, have 
been found in various places and oftisn in considerable depths, 
especially between submarine ridges and islands; between the 
