38S The American Geologist. Juik', i897 
between the fauna? of the Trenton and Galena limestones. 
The constant deep-reaching and equall}^ directed character of 
the water motion also excludes its having consisted of local 
wind-drifts. 
These considerations have induced the writer to see in the 
observed movement of the water, a part of the general ocean- 
ic circulation and to suppose the passing of an E. N. E.-W. S. 
W. current along the southern coast of the Adirondack land- 
area. It is probable that the obstacle offered by this project- 
ing land decreased the depth of the current and made thus 
the phenomenon of the arrangement of the fossils especially 
visible in the Mohawk river region. As the transporting 
power ol; the currents has been found to extend to a depth of 
300 fathoms, there can be no doubt that the influence of the 
supposed current could have reached to the depth in which 
the graptolite-shale of the Utica epoch was deposited. 
It might seem unreasonable to speak of a strong, deep- 
reaching current action in an age, in which the distribution of 
the fossils generally has been regarded as proving the absence 
of all diversity of climate and of oceanic temperature.* But, 
accepting the ftrst of the two rival theories as to the cause of 
the oceanic circulation, namely, that which claims that the 
latter arises entirely from differences of temperature and sal- 
inity, it will be easily seen, that the latter again are due to 
differences in the insolation on the surface of the ocean. But 
the insolation must always have been different at different 
latitudes, and this unequal distribution of solar heat must al- 
ways have disturbed the equilibrium of the spheres and hence 
must have constantly produced currents to restore the e'qui- 
librium. Accepting the other view', that oceanic currents are 
caused by the atmospheric circulation, would be only insert- 
ing a new link into the chain of conclusions, as the circula- 
tion of the air itself is due to unequal insolation. 
Investigators like Dana, therefore, have always regarded 
the existence of a system of oceanic circulation, similar to 
the present, even in Palaeozoic times, as self-evident. Danaf 
for instance, in discussing the presence of the Trenton lime- 
*Barrande has distinguished two bands in the Cambrian of Europe 
which are thought to represent climatic zones. 
tJames D. Dana; Manual of Geology, 3rd ed., p. 208. 
