238 Scientific Intelligence. 



faulting. And especially is it difficult to discriminate between 

 the broad horizontal thrusts which occur there and deposition 

 overlaps. The work of the past summer has enabled me to make 

 this discrimination in many cases, and has convinced me that the 

 unconformity observed between the sandstone and underlying 

 formations is due generally to deposition overlap and not to 

 faulting. This implies a long period of deformation and erosion 

 between the time represented by the Rockmart slate (probably 

 Hudson River) and the Frog Mountain sandstone, an interval 

 represented elsewhere by the deposition of the Rock wood (Clin- 

 ton, etc.) which formation to the southward contains heavy beds 

 of conglomerate. This conclusion also strengthens the view, sug- 

 gested by the fossils mentioned above, that the sandstones of 

 Frog Mountain are of Devonian (Oriskany) age. The uplift 

 which occasioned the unconformity appears to have been along a 

 N.W.-S.E. axis with rather sharp folds transverse to the axis of 

 uplift and in a general way coinciding with folds and faults 

 developed at a much later date. 



2. Marine shell fragments in drumlins near Boston; by 

 Warren Upham. (Communicated.) — The very interesting paper 

 by Mr. R. E. Dodge in the February number of this Journal 

 (pp. 100-104) draws attention to the greater number of species 

 of Pleistocene fossils found in the section of Winthrop Great 

 Head than in any other drumlin of the Boston Harbor area. This 

 is true, but in a less degree than is supposed by Mr. Dodge, as I 

 am able to state from unpublished observations by Mr. Warren 

 W. Herman of Boston, and from a recently published memoir by 

 Prof. W. O. Crosby (Geology of the Boston Basin, vol. i, Part I, 

 Nantasket and Cohasset, in Occasional Papers of the Boston 

 Society of Natural History, vol. iv, 1893). During the summer 

 of 1891 Mr. Herman spent much time in Winthrop in seai*ch for 

 these marine shells, occurring chiefly as glacially broken frag- 

 ments, in the drumlin sections of Great Head and Grover's Cliff; 

 and he succeeded in finding in each of these hills eight of Dr. 

 Stimpson's original list of fourteen species. Six of this list, 

 namely, the first, second, sixth, and the final three, as given by 

 Mr. Dodge on page 100, were not certainly identified. The 

 most noteworthy difference between these fossils common to the 

 two sections, as shown by Mr. Herman's collections, is the fre- 

 quency of Mi/a arenaria in Great Head, while it is very rare in 

 Grover's Cliff. In the Great Head section he also found frag- 

 ments of young specimens of Seapharca transversa, several 

 small specimens (about ^ inch long) of a Lunatia, one specimen 

 of Bicccinum undatum (evidently dead and worn, as if cast 

 ashore from outer and deep water, before it was enclosed in the 

 till), one small Ilyanassa obsoleta, and one Crepidula plana Say, 

 the last being lodged inside a shell of the Urosalpinx cinerea. 

 Three of these additional species, and probably also the Lunatia, 

 are remarkable in being the same with those of Mr. Dodge. 



