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CAPE COD GEOLOGY 



Cambrian upward. A large specimen of this scolithoid sandstone or quartzite 

 was found several years ago on the beach at Marshfield, on the opposite side 

 of Cape Cod Bay. 1 



The fossilferous Cambrian pebbles that are scattered widely on the south 

 coast in the glacial drift or in the rearranged drift of the modern sea beaches 

 have doubtless been dragged out of the coarse conglomerate of the Carboniferous 

 rocks of southern Massachusetts and Rhode Island. The pebbles in this con- 

 glomerate are not only more numerous but larger toward the southern side of 

 the field. No such pebbles have been found in the conglomerate along the 

 northern border of the district, in the area about Norfolk, or in the area of 

 Roxbury conglomerate near Boston. These Cambrian pebbles were evidently 

 carried southward beyond the present coast in Carboniferous time, from a 

 land where quartzite crops out. The Cambrian pebbles on Nantucket and on 

 the outer part of Cape Cod were therefore probably brought by one or more 

 ice sheets from beds of Carboniferous conglomerate that lay under Massachusetts 

 Bay or on the floor of the Bay of Maine. The conglomerate doubtless derived 

 them from the lost land on the south, southeast, or southwest, which was reduced 

 to a peneplain in middle Mesozoic time and covered in Upper Cretaceous time 

 with sediment that still remains off the south coast in the New England Islands. 



At least three erratic fossiliferous Devonian pebbles have been found in 

 southeastern Massachusetts. The first one I found in the moraine on Marthas 

 Vineyard as long ago as 1888. A slabby greenish-gray quartzite or semi-quartzite 

 found in the middle of the island just west of the village of West Tisbury, near 

 a pond on the Tiasquam River, was submitted to Prof. Henry Shaler Williams, 

 who reported on the material as follows : 2 



Examination of the fossils shows two species, one an Orthis, which presents close resem- 

 blance to 0. multistriata, and a fragment of what I take to be a Spirifera. It is less than half 

 of a dorsal valve, but what there is of it closely resembles that part of a form which occurs in 

 the Maine so-called Devonian faunas and which is generally called Sp. cyclopteris, but is shorter 

 than that species generally is in New York. I am inclined to think it is a representative of the 

 fauna found in the Gaspe sandstone. Correlated with Schoharie and Esopus of New York. 

 Similar rock with this fauna occurs in the northwestern part of Maine about Moosehead Lake, 

 and probably deposited farther south, though I know of no region for it. 



1 U. S. Geol. Survey Mon. 33, pp. 110, 112, 1899. On the distribution of fossiliferous Cambrian pebbles 

 in the Carboniferous conglomerates of the Narragansett area and on the beaches and in the glacial drift 

 south of this coal field, see also W. B. Rogers, Proc. Boston Soc. Nat. Hist., 7, 1861, pp. 389-391; W. O. 

 Crosby and G. H. Barton, Am. Jour. Sci. 3d ser., 20, 1880, pp. 416-420; C. D. Walcott, Am. Jour. Sci. 

 4th ser., 1898, pp. 327-328. Crosby and Barton noted the occurrence of Scolithus pebbles in the Carbon- 

 iferous conglomerates near Newport, R. I., such pebbles are not uncommon on the beaches of Vineyard 

 Sound. 



2 Letter to Director C. D. Walcott dated New Haven, Conn., April 10, 1889. 



