VI 



rocks at Hell Gate and about Astoria. The greater portion of the 

 north side covered with till of various thicknesses, in some places the 

 yellow gravel, or preglacial drift coming to the surface. On the 

 slope of the southern hills a large amount of disintegrate till brought 

 down by the streams and rain, a small surface area made up of the pre- 

 glacial drift, and finally the alluvial sand and the various sand marsh 

 components of the south shore. 



A certain amount of attention has been given to the soil because it 

 is so closely correlated with the historical geology of the island which 

 has been so ably investigated by Drs. N. L. Britton and A. Hollick. 



It would needlessly extend this account to go at length into the 

 many valuable discoveries of Drs. Britton and Hollick which have 

 served to prove that underlying the whole of Long Island and extend- 

 ing up along the chain to Cape Cod there are Cretaceous or post- 

 Cretaceous strata. Yet the facts are of such interest and have such an 

 important bearing on some features of the flora of the island that a 

 brief quotation of some of their discoveries is desirable. 



'^During Cretaceous and Tertiary times a series of fresh water or 

 estuary and marine deposits (clays, sands, gravels and marls) was laid 

 down along the eastern borders of the North American Continent. 

 About the close of the Miocene, or the beginning of the Pliocene, an 

 era of elevation began, which finally raised them hundreds, in places 

 thousands of feet, above their present level, forming a wide coastal 

 plain, which extended over the whole area where we now find them 

 and for a considerable distance eastward, into what is now part of the 

 bed of the Atlantic Ocean. On the land side this plain was bounded 

 by the crystalline and triassic rocks of Connecticut, southern New 

 York, Pennsylvania and southward as may be seen by an examination 

 of any good geological map of the eastern United States. The evi- 

 dence of its extension around Massachusetts and Rhode Island are now 

 almost obliterated, but there seems to be every reason to believe that 

 its land limits were approximately the coast line of the present day. 

 In fact, a small isolated portion of the old coastal plain still exists 

 apparently in the region of Marshfield, Mass., as indicated by E. 

 Hitchcock in 1841,'!^ and recently by N. S. Shaler.f Further north 

 than Massachusetts, so far as I am aware, it is not even indicated, and, 

 except for the presence of the well -recognized submerged plateau off 

 our eastern shores, all further trace of the former coastal plain is lost. 



* Final Report Geol. Mass., ii, 427. 



t Tertiaiy and Cretaceous Deposits m Eastern Massachusetts, BulL GeoL Soc. Am., 



I, 443. 



