20 



CAPE COD GEOLOGY 



they are the stomach stones or gastroliths of seals. Sir John Murray x states that 

 both seals and penguins carry to sea in their stomachs large numbers of stones 

 and pebbles, which sealers call ' 'ballast." He remarks that ' 'these animals may, 

 therefore, to some extent distribute rock fragments to great distances from the 

 land; should any of them be killed or die at sea their soft parts might be entirely 

 removed in solution, and even their bony structures might be entirely removed, 

 while the stones and pebbles contained in their stomachs would remain as a 

 part of the deposit." 



Moseley 2 too states that ' 'stones are found in all seal stomachs, apparently 

 just as in those of penguins." 



GASTROLITHS AT DUXBURY AND MARSHFIELD 



The Miocene deposits of the mainland in Duxbury and Marshfield were 



first described by Hitchcock in 1833. 3 



Here were found a very perfect shark's tooth, the case of a small species of Venus, and the 

 same species of Turbo that occurs at Gay Head. In another specimen of Venus, in the cavity 

 occupied by the hinge, is a small quantity of greensand, exactly like that at Gay Head, which 

 proves satisfactorily the identity of the marsh mud and the greensand; and that the greensand 

 of Gay Head is identical with that in England a comparison of specimens shows. 



Hitchcock again visited the greensand area in Marshfield and Duxbury in 

 1837, when certain wells were open, and found that greensand had been thrown 

 out from at least three wells. 4 



A chemical analysis of the greensand from Marshfield by Dr. S. L. Dana 

 was published by President Hitchcock in the same report. 6 



In the Final Report on the Geology of Massachusetts, published in 1841 

 (page 91-92), Hitchcock reprinted, without additional comment, the statements 

 concerning the greensand in Duxbury and Marshfield. 



In 1850, Dr. Jackson, 6 of Boston, stated, in remarks on the Tertiary deposits 

 at Marshfield, that a shark's tooth, a cetacean vertebra, lignite, and the cast of 



1 Report on deep-sea deposits. The Voyage of the Challenger, pp. 323-324. Zoology of the Challenger 

 Expedition, pt. 8, pp. 126-127; also Turner, Report on Seals, Zool. Challenger Exp., pt. 68, p. 136. 



2 Notes by a naturalist made during the voyage of the Challenger, revised edition, New York and 

 London, 1892, p. 178. Moseley notes that penguins are eaten by seals (p. 164); hence seals may not vol- 

 untarily take up pebbles from the shore or the bottom. 



3 Hitchcock, Edward, Report on the geology, mineralogy, botany and zoology of Massachusetts, 

 pp. 199-201, Amherst, 1833. 



4 Hitchcock, Edward, Report on a reexamination of the economical geology of Massachusetts, p. 76, 



Boston, 1838. 



6 Hitchcock, Edward, op. cit., p. 77. 



6 Jackson, Charles T., Proc. Boston Soc. Nat. Hist., 3, pp. 323-324, 329, 1851; also Proc. Am. Assoc. 

 Adv. Set, 4, 1851, p. 251. 



