On the Physical Geology of the United States, §c. 15 
much probability a current from the north. Other evidences of 
such a current have been observed. 
10. The great coal formations of the eastern and central por- 
tions of the United States are based upon a sandstone which, at 
its outcrop on the edges of the coal basins, is a conglomerate or 
coarse sandstone, and sometimes a very coarse puddingstone, 
while towards the centre of the basin itis much finer. This 
fact indicates a stronger flow on the exterior of the coal forma- 
tion than within its area. This is in strict conformity with the 
supposed origin of the coal formation—being formed in eddies, 
and that stronger currents immediately preceded the coal forma- 
tion. Periods of comparative repose, with gently varying cur- 
rents, preceded and succeeded the deposition of the conglome- 
rate, and strata of slate, shale, sandstones, limestones, &c. were 
extensively and abundantly deposited. 
11. The tertiary and upper secondary formations of the east- 
ern and southern parts of the United States, and between the 
Mississippi River and the Rocky Mountains, may be attributed to 
the action of the Gulf Stream, and to a similar current on the 
western side of the Mississippi valley, before our continent was 
raised to its present level.* 
Examples might be multiplied indefinitely in illustration, and 
much space would be required for a full development of the sub- 
jects of this paper. I have treated of general principles and 
masses of facts as connected with the physical geology of the 
sedimentary rocks of the United States, without going into de- 
tails on local geology. 
All that is known in relation to the sedimentary rocks of the 
United States, from the oldest transition to the quaternary forma- 
tions, harmonizes, I believe, with the views here advocated of 
the causes of their transport, deposition, distribution, and organic 
contents; while on the other hand, I am not aware of any argu- 
ment that can be urged in opposition to its probable truth. 
We may therefore conclude, that the great masses of the sedi- 
mentary rocks of the United States have been deposited by 
marine currents before the continent fully emerged from the 
ocean. 
* Natural History of New York, Part IV, Geology of Ist District, by W. W. 
Mather, pp. 229, 274, 292. 
