Dana — Submarine Hudson River Channel. 435 



have a width of 5,000 to 10,000 feet. The best way to realize 

 the truth as to the form and pitch of the channel is to draw 

 diagrams with the actual proportions ; not to refer to an exag- 

 gerated and deceiving plaster model. 



Terminal part of the Channel, at the margin of the Atlan- 

 tic-border plateau. — The remaining part of the channel, but 

 25 miles long, is beyond question the work of river-erosion. 

 Only four miles from the last of the 41-fathom soundings, comes 

 the 52, indicating a mean slope between of about V6\ feet a 

 mile ; after the next 2-| miles, comes an 183-fathom sounding, 

 showing a mean pitch off of 315 feet a mile ; in 5-J- miles more, 

 a 277-fathom sounding, corresponding to a pitch of 103 feet a 

 mile ; and then to others deepening the gorge a little more 

 slowly to 471 fathoms ; and this depth exists about in a line 

 with the 80-fathom bathymetric line. The depth in the cut at 

 this point is hence nearly 2400 feet below the region adjoining. 

 This gorge cannot be pronounced canon like without more 

 facts from soundings ; for the pitch in the sides according to 

 the existing data does not exceed 1:5. Still it affords strong 

 evidence of river origin, and, therefore, that the whole of the 

 channel, up to New York Bay, was once the course of the 

 Hudson River. At the same time it makes it strange that the 

 river channel should have flattened out over the loose sands and 

 muds of the 40-foot to 45-foot level when so tremendous a 

 plunge was before it, unless the conclusion is a right one that 

 tidal scour is the cause of the present features from the outer 

 limit of the 41-foot level upward to the Bay. 



Time of the emergence. — The remarks on the " submerged 

 Hudson River channel 1 ' in my Manual of Geology are intro- 

 duced in the account of the Jura-Trias formation of eastern 

 North America. The absence of marine fossils from the Jura- 

 Trias had led to the inference that the sea-border of the period 

 for some distance out was more or less emerged. It was not 

 inferred that there was then a great elevation of the Conti- 

 nental border — for the large size of the Jura-Trias estuaries 

 proved the contrary to be true ; but that there was simply a 

 bending upward and emergence of the coast-region which car- 

 ried the sea-bottom above the water-level out to the 100- fathom 

 line, or farther. I have referred the emergence to a low 

 geanticline begun long before the Carboniferous era, for no 

 Carboniferous-Devonian or Upper Silurian rocks of Atlantic- 

 border origin are known. The Hudson River as it left the 

 Palisade Estuary (for the region from New York to Tomkin's 

 Cove opposite Peekskill, appears to have been part of one of 

 the estuaries) flowed — sluggishly it may have been — across the 

 emerged sea-border, and thence emptied into the Atlantic. It 

 was long after the Jura-Trias period had passed, and even after 



