250 



CAPE COD GEOLOGY 



Mr. Blake's notes and the samples he obtained afford the following data: 



A sample taken about 200 feet down consisted of broken shells, in fragments 



from 10 to 12 mm. long, stained yellow to brownish with iron oxide; apparently 



existing species of molluscs; also small pebbles and fragments of rock, among 



which are recognizable a red shale, blue slate, granitic quartz grains, quartz 



porphyry, whitish quartzite, and a much decomposed ferruginous rock. The 



rock is typically rearranged glacial gravel like that found at several horizons 



in the Pleistocene series. 



Dr. Dall, to whom the fragments of shells were submitted in 1915, identified 



them as follows: 



Balanus sp. 



Lunatia, probably L. heros Say. 



Venus, doubtless V. mercenaria L. 



Macoma, probably M. balthica L. 



Spicula solida or similis, of the present fauna. 



Eckinarachnis sp. 



These identifications are only tentative. According to Dall the horizon is 

 probably that of the upper bed at Sankaty Head, Nantucket. 



A gray sandy clay containing small grains of yellowish quartz, scales of 

 muscovite, and minute particles of a black mineral, probably magnetite, was 

 encountered at a depth of 300 feet. The clay is free from compound unde- 

 composed minerals, such as the feldspar found in the New England glacial 

 drift deposits, but is apparently an intercalated member of the shell-bearing 

 series of coarse sand and fine gravel. 



Mr. Blake collected from material brought from the depth of about 360 

 feet waterworn yellowish fragments of a sand dollar (Eckinarachnis sp.). 



This scant record of the well at Provincetown seems to indicate that the 

 Sankaty sand there is at least 160 feet thick and that it lies 200 to 360 feet below 

 the surface. It has been reported that Area transversa was found in an artesian 

 well drilled many years ago at Provincetown to a depth of 120 to 200 feet below 

 the surface. 1 This well was drilled near the shore of the harbor at or near the 

 long wharf. Area (Scapharca) transversa is still living in the sea about Marthas 

 Vineyard, Nantucket, Chatham, and Wellfleet. Its reported occurrence at a 

 depth of 120 feet in this artesian well — a depth about 80 feet nearer the surface 

 than the depth at which the shells reported from a well drilled in 1905 — is 

 doubtful in view of the uncertainty concerning the dip of the Sankaty sand 

 beneath Provincetown. 



1 W. G. Binney (editor) and Augustus A. Gould, Report on the Invertebrata of Massachusetts, 

 Boston, 1870, p. 149. 



