THEORIES OF ORIGIN 155 



Merrill in the same folio * has carried the theory to its extreme. Not 

 only are the windings of Spuyten Duyvil creek and the Harlem river 

 supposed to follow the course of a belt of limestone, but even Long 

 Island sound near New York is supposed to have the same origin. 

 These assumptions are based largely on the " white residuum " obtained 

 from dredgings by the dock department^ 



If we grant that this white material may be the residual product from 

 the solution of dolomite, its presence at the bottom of a swift tideway 

 like that of the East and Harlem rivers can have but little significance, 

 when it is remembered that the Harlem flows between limestone walls 

 for a considerable portion of its course. 



In a recent extended report on the Glacial and post-Glacial history of 

 the Hudson valley, Peet J has favored the view that the Hudson water 

 front was in post-Glacial time a lake impounded by a moraine, the inlet 

 now existing through the moraine having been formed by the cutting 

 down of the lake outlet so as to form the present Narrows. He says : 



" In conclusion, it may be stated that while no single argument seems to be fatal 

 to the salt-water hypothesis accounting for the Hudson water body, unless those 

 drawn from the phenomena on the outside of the moraine be such, it is likewise 

 true that the facts are not fatal to the lake hypothesis, unless the sponge spicules 

 reported from Croton represent salt-water species. Aside from these sponge spic- 

 ules, the weight of the evidence seems to be in favor of the lake hypothesis." 



Julien, in discussing the faults on the island, has called attention to 

 the evidence of the transverse fracturing of the rock at Spuyten Duyvil 

 creek : 



"At other localities, as, for example, at the huge pit on Spuyten Duyvil creek, 

 portions of the hornblendic rock are traversed by innumerable veinlets of quartz 

 or pegmatite, indicating a shattered or even brecciated mass." 



Form of the Rock Floor beneath the New York Water Front 



generally accepted view 



From the above review it will appear how generally Dana's theory has 

 been accepted and also how little evidence for it has been adduced. It 

 has come to represent, however, a body of opinion to some extent in- 

 herited, and it probably owes its favorable acceptance largely to the fact 

 that the principal channels about New York island trend approximately 



*0p. cit., p. 4, columns 3 and 4. 



t Merrill: Op. cit., p. 4. See also F. J. H. Merrill and D. S. Martin: Note on the colored clays 

 recently exposed in railroad cuttings near Morrisania, New York. Trans. New York Acad. Sci., 

 vol. ix, 1889, pp. 45-46. 



X Charles Emerson Peet : Glacial and post-Glacial history of the Hudson and Champlain valleys. 

 Jour. Geol., vol. xii, 1904, pp. 415-469, 617-660. 



