about the head of the Missouri, &c. 243 
physical break occurring in the sediments. 
Will not these statements go far to show that the estuary de- 
posits ushered in the dawn of the Tertiary epoch and induce the 
belief that they belong to the first part or Eocene period? This 
point 1s an important one to establish, on account of its bearing 
upon the history of the physical development of our western 
continent. . 
ave no evidence, so far as I know, of long continued 
deep-water deposits in the west, until far up in the Cretaceous 
Tiod _ If we examine the Potsdam sandstone we shall find that 
Where it reaches its greatest force, the lower portion is comp 
{uite compact with fucoidal markings, ripple-mark, &c. Every- 
> are most abundant examples of oblique laminze of deposit, 
and ripple and wave-markings—evidences of shallow waters. 
During the long period that elapsed between the deposition of 
ot aniest part of the Silurian epoch and the commencement 
ment: | 
and all the proofs of shallow as well as turbulent waters 
shown. We then pass up through the red arenaceous de- 
