1896.] NEW YORK ACADEMY OF SCIENCES. 23 



to which it has consistently adhered, while the westerly depres- 

 sion has been caused by the small stream now occupying it ; and 

 that the brook has excavated this valley at a little slower rate 

 than the Bronx has its present one. But when one sees the size 

 of the west depression and the insignificance of the present 

 stream it is clearly impossible that such could have been the case. 



It will at once occur to all who are familiar with the problems 

 involved in the river drainage of the State of Connecticut* 

 that both the Housatonic and the Connecticut rivers have left 

 what appear to be their natural channels and have turned east- 

 ward through ridges of gneiss, but the diversion of the Bronx, 

 with its 50 or 60 feet of gorge and its potholes, is not a phe- 

 nomenon of the same magnitude with that of the Connecticut, 

 the bottom of whose gorge lies four hundred feet below the old 

 Cretaceous peneplain. The earlier valley of the Bronx doubtless 

 represents its Tertiary erosion in the Cretaceous peneplain of 

 Westchester County, while the gorge is of Glacial and Post- 

 glacial development. 



The portion of the geological history of the Bronx, therefore, 

 that is discussed in this paper,' is so recent, that it has not been 

 felt to be necessary or appropriate to review the general produc- 

 tion of the Cretaceous peneplain, whose stumps now form our 

 singularly even hilltops and horizon line, but in the paper cited 

 below its development will be found fnll}^ set forth. f The re- 

 cent geologic history of the neighboring coast has a more direct 

 bearing. As regards Long Island Sound, Professor Uana| has 

 supplied some very important points in the record. It is alto- 

 gether probable that Long Island Sound was a river valley dur- 

 ing a part at least of the Glacial Period, certainly before the ice 

 covered it and built up the Long Island moraines. A well 

 marked channel is still shown by soundings along the north 

 shore of Long Island, and it is necessary to assume an eleva- 

 tion of 100 ft. above its present position in order to account for 

 these conditions. Other channels are also indicated, now, of 

 course, drowned out by the Sound and choked up as regards 

 some of their old outlets by drift. 



A few months after the publication of Professor Dana's paper, 

 Dr. F. J. H. Merrill § recorded and interpreted evidence that in- 



*See in this connection W. M. Davis, Topographic Development of the Triassic 

 Formation of the Connecticut Valley, Amer. Jonr. Set., June, 1889, 423. H. B. Kiim- 

 mel. Some Rivers of Connecticut, Journal of Geology, Vol. I., 371, 1893. 



fW. M. Davis. The Geological Dates of Origin of Certaia Topographic Forms on 

 the Atlantic Slope of the United States. Bulletin Geological Society of America, II. 

 Mb, 1891. 



X J. D. Dana. Long Island Sound in the Quaternary Era, with Observations on the 

 Submarine Hudson River Channel. Amer. Jour. Sci., December, 1890, p. 425. See 

 also John Bryson. Amer. Geol., November, 1896, p. 329. 



§F. J. H. Merrill. Post-glacial Historv of the Hudson River Valley. Amer. .Tour. 

 Set.', June, 1891. p. 4(30. 



