780 ABSTRACTS OF PAPERS 



MAQOTHY FORMATION OF THE ATLANTIC COAST^'^ 

 BY A. B. BIBBINS 



(Ahstract) 



So far as Long Island is concerned, the paper will regard the Magothy as 

 present in force, its contact with the Raritan (of land as now defined) lying 

 along the north shore of the western half of the island. The upper limits of 

 the formation, which are so well defined to the southward, may prove more 

 difficult to determine here, owing to the fact that the superjacent Matawan 

 and its overlying formations appear to have taken on, along with their marked 

 change in strike, Magothy-like characters, as, indeed, the Matawan has already 

 begun to do as far south as Atlantic Highlands. The greensands of the upper 

 portion of the Melville section and those of the deep wells toward the eastern 

 end of the island will probably prove to lie even higher than the Matawan, 

 but the most impressive feature of the Long Island well and other sections 

 along the belt where the greensand marls might be expected is the almost 

 universal absence of gtauconite beds, and the occurrence in their stead of ma- 

 terials lithologically similar to those of the subjacent Magothy — indicating 

 either more moderate depths during sedimentation than those of their con- 

 temporaneous deposits to the southward, or other changes of conditions which 

 brought different sediments and largely eliminated foraminifera. The thick- 

 ness of the Magothy beds on Long Island seems likely to reach considerably 

 more than 100 feet. It is certain that the formation thickens rapidly toward 

 the northward across New Jersey to a maximum of 100 feet on the south 

 shore of Raritan Bay. The Magothy is an important physiographic factor. 

 Its influence as a bay, island, hill, and drainage-line former is impressively 

 shown all along our coast. As an economic factor one finds that one of the 

 greatest series of sand quarries in the world — on the west shore of Hempstead 

 Harbor, L. I. — an important source of building sand for Greater New York, 

 lies to a goodly extent in the Magothy formation, while the very general arena- 

 ceous lithology and loose bedding of the formation render it an important 

 underground water-bearer. 



AOE OF THE CALCIFER0V8 FORMATION OF THE MOHAWK VALLEY, NEW 



YORK 



BY E. O. ULRICH AND H. P. GUSHING 



{Al)stract) 



The Little Falls dolomite of the Mohawk Valley is found to consist of two 

 distinct and unconformable formations. The lower and thicker of these is a 

 dolomite formation which, in the eastern sections, is underlaid by the Pots- 

 dam sandstone, and the two grade into one another through passage beds. To 

 the west the Potsdam and passage beds disappear and the dolomite rests 

 directly on the pre-Cambrian. This dolomite the authors regard as of Sara- 

 togan (Ozarkian) age. They have traced it into the Champlain Valley, and 

 find that it there constitutes division A and the lower half of division B of the 

 Beekmantown (Calciferous) formation, as characterized by Brainerd and 

 Seely. 



" Read by title, In the absence of the author. 



