SOME FEATURES OP STATEN ISLAND DRIFT 3 



material too fragmentary or poorly preserved for accurate determination. From 

 an examination of these fossils we are able to say with absolute certainty that every 

 geological horizon in the Paleozoic, from the Potsdam to the Hamilton, is repre- 

 sented in our drift boulders, and in the Mesozoic both Triassic and Middle Cre- 

 taceous. The Tertiary is but sparingly present, but is probably iipper Miocene or 

 Pliocene. 



There are, therefore, two important breaks in the sequence — one between the 

 Devonian and the Triassic and another between the Triassic and the middle Cre- 

 taceous. Carboniferous Jurassic and Lower Cretaceous rocks areentirely wanting. 

 If, now, we take the compass direction of the glacial striee on Staten island, which 

 have been determined to be about north 13 west to north 20 west, and extend 

 them northward, they may be seen to cross the outcrops of the several horizons 

 whose fossils have been found in the drift material, while, on the other hand, 

 throughout the same region to the northward no indication of either Carbonif- 

 erous Jurassic or Lower Cretaceous rocks has ever been found. 



It is probably not necessary to quote the entire list of fossils, but it may be of 

 interest to know that the majority of the Paleozoic species are Lower Helderberg 

 in age, with Oriskany and Schoharie next. 



J trypa reticularis, L. ; Eatoyiia peculiar is, Conr. ; Fenestella nervia. Hall; Meristella 

 nasuta, Conr. ; Spirifer arrectus, Hall ; S. arcuosus, Conr. ; S. macropleurus, Conr. ; 

 Stropheodonta beckii. Hall, and Strophomenarhomboidalis, AVahl., are among the most 

 abundantly represented' species of brachiopods. 



The only Triassic species is an Equisetum, provisionally determined as E. rogersii, 

 Schimp. The Cretaceous fossils are all plants, with the exception of seven mol- 

 lusks. The two Tertiary species are plants, and the one Quaternary is a mastodon's 

 tooth. 



There are also some features of the drift worth noting, besides those relating to 

 the character of the material. ■ ■ 



The structure of the moraine where it rests on the serpentine ridge is different 

 from the structure of that part which rests on the plain region. In the former 

 locality it is composed entirely of transported material brought from the mainland, 

 and consists of glacial till, gravels, and occasional deposits of clay. In the latter 

 locality, however, it consists of a core of contorted Cretaceous strata, moved but 

 little from their original position in the island, on top of which the true morainal 

 debris rests. This character of the moraine on the plain region is identical with 

 its character to the eastward, on Long island. Block island, Marthas Vineyard, and 

 the Elizabeth islands, and is manifestly due to a squeezing upward of: the inco- 

 herent strata of the coastal plain by the advancing ice-front and then to the depo- 

 sition of the glacial debris over the contorted ridge thus formed. 



Incidentally these facts also prove, or at least strongly indicate, that no Creta- 

 ceous strata ever existed to the north of the serpentine ridge of the island, as no 

 fragment of material which could be even provisionally identified as Cretaceous in 

 age has ever been found in that portion of the moraine which rests on the ridge, 

 whereas it is abundant throughout the moraine in the plain region. 



Finally, it may be of interest to note how the preglacial topography modified 

 the advance and direction of the ice at one particular point. If the course of the 

 moi'aine is traced, it will be found that the most prominent northward-extendino' 

 sinus in the moraine is immediately south of the highest point on the serpentine 

 ridge. This indicates almost conclusively that the high ridge checked the advance 



