CONNECTICUT RIVER SANDSTONE. 31 



water, there is a remarkable difference to be observed among the successive 

 impressions, resulting from variable density of the stratum upon which the animals 

 walked. I have observed instances where the first of a line of footprints was 

 flattened. After a step or two the impressions were tuberous; and, pursuing the 

 line farther, they became imperfect, and finally disappeared altogether. When 

 extensive surfaces are exposed in situ, these modifications are always apparent; 

 and it frequently happens that the best and worst specimens of footprints occur 

 together upon the same surface. 



Probable sources of the Waters of the /Sandstone Basin. — It is an interesting subject 

 of inquiry, to determine whether the waters of the ancient sandstone basin were 

 derived from marine, lacustrine, or fluviatile sources. The topography of the valley 

 of the Connecticut River that corresponds to the area of the sandstone deposition 

 suggests the hypothesis of an estuary or inland sea, connecting with a distant 

 ocean ; but, however that might be, it is certain that the level of the waters 

 was not stationary, but was subject to considerable fluctuations. It is unsatis- 

 factory to ascribe this disturbance to tidal influence alone; for under ordinary 

 circumstances it is impossible that the stratum should be sufficiently consolidated 

 in the interval between the ebbing and flowing of tides to retain impressions, 

 and, moreover, as has been stated, the stratum often bears unequivocal evidence 

 of being impressed at distinct and distant intervals of time, while it was acquiring 

 an increasing degree of solidity. This fact cannot be disposed of upon the suppo- 

 sition of tidal agency; it is manifest that the periods of fluctuation were much 

 longer than those occurring between the falling and rising of tides. There is 

 abundant evidence that copious rains watered the earth during the sandstone era ; 

 and it is not improbable that the atmosphere was more highly charged with 

 moisture than in the present day. The materials of the sandstone rock are 

 composed exclusively of the detritus of antecedent rocks, which were broken, 

 rounded, or pulverized by some mysterious agency, that could only be moved 

 to the place of their receptacle by the force of powerful currents. The coarser 

 parts were lodged in the remote depths, and constituted the unstratified masses 

 of the sandstone rock, while the finer parts were deposited upon this basis in 

 regular stratification. Hence the presumption is at least plausible, that the 

 accumulated waters of the sandstone basin constituted a narrow estuary or inland 

 sea. having its upper or northern limit at the place now known as Turner's 



