Spencer — Great Canyon of the Hudson River. 9 



plateaus. I may have too strongly represented the feature on 

 the map, but it is not one of special importance. 



Constitution of the Contiiiental Shelf. 



All our classic teaching tells us that, during the earlier and 

 middle Mesozoic era and far into the Cretaceous period, the 

 continent here was so elevated and subjected to denudation that 

 the sediments were carried far seaward. We cannot go into 

 the question as to their covering the continental slope, but it 

 would seem that the continental shelf now submerged was sub- 

 jected to the same conditions as those now underlying the 

 coastal plains of the adjacent lands. On these we learn that 

 besides a few hundred feet of Potomac sands, which probably 

 thin out, there are deposits of sand, greensand, clay and clay 

 marl of the upper Cretaceous formations reaching a thickness 

 of 800-1100 feet. Then follow some Eocene sands succeeded by 

 clayey, marly and sandy beds belonging to the Miocene beds. 

 These occur in an artesian well boring at Atlantic City, reach- 

 ing to a depth of 1400 feet (without penetrating the series or 

 the limited Eocene sands or obtaining water at the lower depths 

 though somewhat higher fresh water occurs, indicating the 

 leaching out of the salt sea water during an epoch of elevation). 

 All below 265 feet is Miocene. This upper part is composed 

 of sand gravel and clay, which may represent important features 

 requiring a word of explanation. Of red gravel sand and stiff 

 clay loam are composed both the Lafayette and Columbia forma- 

 tions, each of which is a thin sheet except where filling valleys. 

 The Lafayette is provisionally regarded as belonging to the end 

 of the Pliocene period, occurring below morainic material as I 

 have seen in New Jersey. But it has been enormously denuded. 

 The Columbia formation (now subject to subdivision) is the 

 material of the Lafayette redeposited, and overlies the drift, 

 with its surface only moderately sculptured. I should suspect 

 that at Atlantic City is a buried channel filled mostly with these 

 deposits of the Columbia period, capped with more recent 

 alluvium. These upper beds are substantially horizontal, with 

 the Miocene dipping a litttle more. For the details of the 

 Miocene deposits in the Atlantic City well see the paper by 

 Mr. L. "Woolman*. 



Thus not knowing whether these incoherent formations have 

 a greater or less aggregate thickness, beneath the submerged 

 coastal plains, there are only known little over 2200 feet to be 

 accounted for from the adjacent shores. But they have formed 

 the subsurface of the level plains now submerged, and chan- 

 nelled by the drowned Hudson river, and finally incised by 

 *Acad. Nat. Sc, Phil. 1887, p. 339, and vol. for 1890, pp. 132-147. 





