76 J. D. Dana on the origin of some of the 



depositions had reached such a level as to impede the inflowing tide, 

 and thereby give the ascendancy to the river current ; this being 

 favored by the height of the land at the time. 



Of the causes suggested above for the diiference between 

 the lower and upper divisions in the sections, C and D are the only 

 ones that can be entertained; and such a flood would have been 

 sooner or later a natui-al consequence of the melting of the glacier in 

 progress. It would have been a flood enormous in extent and vast in 

 effects ; it may have been not merely an overflow of a few months, 

 but of a period of years. 



(3.) The subdivisions of the layers into subordinate wave-like parts 

 may have resulted from the plunge of the waves that accompanied 

 the tidal or current movements of the waters. Each of these subordi- 

 nate parts is not the Avhole that was formed by the plunge and flow 

 of a wave, but this minus what it lost by the succeeding plunge or 

 plunges — as a little study of figure 1 will make apparent. In these 

 wave-like parts of a bed, the oblique layers usually diverge as they 

 rise upward, as shown in figure 1. The wave struck at the end from 

 which the lines diverge, and as it pushed forward with slackening force, 

 it dropped more and more of the the sands taken up, and so the little 

 layers formed l)y it were made gradually thicker. So much material 

 deposited with one fling of a wave would seem to indicate rapid work 

 in the deposition of the beds. 



The reasons for regarding these and other like beds as depositions 

 directly from the glacier are the following. (1.) Stratified deposits 

 were thus made by the glacier and the waters beneath somewhere 

 about the New Haven region ; and no others exist that can be such. 

 (2.) These beds, consisting largely of interstratified sand and gravel, 

 and in part of layers of coI)ble stones, have characters according pre- 

 cisely with the sup])osed mode of origin. It will be noticed that the 

 layers of cobble stones have not required for their formation, on this 

 view, streams of tremendous magnitude and violence, beyond all 

 physical probability, in order to transport the stones from their place 

 of origin, 50 or 100 miles or more to the north ; the work of transpor- 

 tation was done quietly by the glacier, and they were simply dropped 

 to their places ; much more moderate streams served to sift out the 

 finer material so as to leave the larger stones alone. (3.) These sand 

 and gravel beds could not have been formed like ordinary sand-banks 

 on a sea-shore or in a bay. For the waves and currents, which are 

 the means of piling up such banks, could not have introduced the lay- 

 ers of gravel or cobble stones except they had been furnished by 

 some other agency ; and the amount of sand that the waves move in 



