246 The American Geologist. April, 1892" 
by the erosion and deposition of fresh detritus from the granites 
gneisses, sandstones and other clastic rocks of the mainland, is 
shown by the factthat no decomposable rocks of feldspathic com- 
position exist in the stratum. This view of the origin of some 
of the Tertiary and perhaps earlier Pleistocene gravels of New 
Jersey and Long Island has been advanced by Mr. N. L. Britton * 
It is possible to trace the quartz pebbles and associated cherts 
to a previous cycle of deposition, in which, before the making of 
the Cretaceous beds, the quartz pebbles with the cherts composed 
the finer, quartzose conglomerates of the middle and lower por- 
tions of the Narragansett coal basin. In the coal bearing section 
of these recks, there occur numerous beds which, but for their 
consolidation and black color, closely resemble the Martha's 
Vineyard gravels, the thickness of which is explained by the 
extensive erosion of these antecedent Carboniferous beds. 
Original source of the Cherts: The vein quartz in the Carbon- 
iferous appears originally to have come from the disintegration of 
a terrane thickly set with quartz veins, as Britton has suggested in 
the case of similar quartz pebbles in the coast plain of New Jer- 
sey; but the fossiliferous chert pebbles with identifiable fossils 
clearly. point to a more definite association of rocks, Cherts 
naturally associate themselves with limestones, though rarely with 
sandstones, as in the Oriskany, and with shales; but the occur- 
rence of chert pebbles in the lower Cambrian, siliceous limestones 
of Nahant, makes it seem probable that the Martha’s Vineyard 
cherts were also derived froma calcareous section of the Olenellus 
Cambrian. As yet the nodules of the Nahant horizon have not been 
shown to carry Kthmophyllum and its congeners, yet Louis Agassiz, T 
in 1850, reported finding in them the structure of an Astrewa. 
The locality of lower Cambrian nearest to Gay Head is that of 
the red shales of North Attleboro.{ a distance of fifty miles, but 
no nodules have been observed in the Attleboro section. That 
there is in the southern coast of Massachusetts or Rhode Island 
the seat of an extensive Cambrian section now concealed or 
removed by erosion, is shown by the abundant fragments of Cam- 
brian quartzites found in the coarser conglomerates of the Car- 
*American Naturalist, 1875, XXIII, p. 1035. 
tL. Agassiz: Proc. Am. Acad, II, p. 270; also’ Proc. Boston Soc. Nat. 
Hist., ILI, p. 341, 1850. 
{N.S. Shaler: On the geology of the Cambrian district of Bristol 
Co., Mass. Bulletin Mus. Comp. Zool., xv1, 1888, p. 13. 
