CAPE COD GEOLOGY 29 



material from Gay Head was made in the laboratory of the United States Geo- 

 logical Survey, states that it is made up as follows : 



Phosphoric acid (P 2 5 ) 23.00 



Carbonic acid (CO,) 2.60 



Lime (CaO) 25.73 



Potash (K 2 0) ! 



Soda (Na 2 0) J 



Silica (SiO,) 17.82 



Many of the nodules enclose remains of crabs and casts of foraminifers and 

 of the mollusk Macoma lyelli. This association accords with the statement of 

 F. W. Clarke that "the organic remains which contribute to the formation of 

 phosphorites vary widely as regards richness in phosphates. Bones are the richest; 

 crustacean remains probably come next; mollusks and corals are the poorest." 1 

 The mode of segregation of the phosphate of lime in the nodules does not indicate 

 that they are coprolitic, but the shape of some of them countenance this view. 2 

 Most of these concave-convex, lumpy nodules bear no resemblance to the fusi- 

 form, transversely constricted objects described as coprolites by their discoverer. 3 

 Moreover, the segregations of nodular crust about uncrushed and undigested 

 carapaces and legs of the fossil crab Archaeoplax signifera in the greensand bed 

 shows that the nodulation took place through chemical processes after the de- 

 posit of greensand had been formed. 



Penrose 4 mentions the nodules at Gay Head as ' 'amorphous nodular phos- 

 phates" and states that they have a waterworn appearance and have a hardness 

 of about 3. He states that they give off decayed organic matter when two frag- 

 ments are rubbed together. He further remarks that the nodules are too widely 

 scattered in the bed and hence too expensive to mine for commercial use. 



EASTWARD EXTENSION OF THE MIOCENE DEPOSITS 



Only two patches of Miocene deposits are exposed along this coast, that at 

 Gay Head and that on Nonamesset Island. In addition, however, there are 

 covered beds in Marshfield and Duxbury. Beds of Miocene greensand probably 

 once extended along the coast as a sheet, of which the present patches are rem- 



1 Clark, F. W., The data of geochemistry, 2d ed., TJ. S. Geol. Survey Bull. 491, p. 500, 1911. 



2 See Buckland, Trans. Geol. Soc. London, 3, new ser., pt. 1, p. 234 et seq., with three plates, 1892; 

 also same author in Geology and Mineralogy, 4th ed., 1, pp. 164-176, London, 1869, and 2, Atlas, pi. 17, 

 1870. 



3 See Bertrand, E. E., Les coprolithes de Bernissart, Memoires Musee Royal d'Histoire Naturelle de 

 Belgique, 1, pp. 1-154, pis. 1-15, Bruxelles, 1903. 



4 Penrose, R. A. E., Nature and origin of deposits of phosphate of lime, U. S. Geol. Survey Bull. 46, 

 P. 78, 1888. 



