CAPE COD GEOLOGY 



23 



deposited. The late Miocene sea, therefore, may not have stood above the up- 

 land about Worcester, for if it had reached that height the land to the west 

 would have stood so high that its position could not be harmonized with the 

 indications of shallow water over the remnants of the Miocene offshore deposits. 

 The greensand beds give little indication of the conditions near and along 

 the shore, for they contain no detrital material that can be traced to the Paleozoic 

 rocks of the inland. The pebbles and grains of quartz in the greensand may have 

 been derived from the remnants of Cretaceous beds over which the Miocene sea 

 transgressed after an epoch of Oligocene land. No definite trace of the Miocene 

 shore has yet been recognized and, as the Miocene beds contain no waste derived 

 from the ancient rocks, the marine invasion in Miocene time must have been 

 short and could not have left strongly marked sea cliffs in the crystalline rocks 

 of the upland. 



CHEMICAL ANALYSES OF THE GREENSAND 



The greensand in Marshfield and on Gay Head has never been used in agri- 

 culture, so its chemical analyses are incomplete. Three analyses that have been 

 published are reprinted below, along with analyses of other greensands. 











Chemical Analyses of G 



reensand 







Constituents 



l 



2 



3 



4 



5 



6 



Si0 2 . . . 







56.70 



49.23 



51.25 



50.85 



A1 2 3 











13.32 



7.11 



7.25 



8.92 



Fe 2 3 











20.10 



20.89 



20.72 



21.40 



FeO . 













3.00 





1.66 



MnO 











tr. 



tr. 







CaO . 







0.65 



1.09 



1.62 



tr. 





1.26 



MgO 











1.18 



3.44 



5.98 



3.13 



Na 2 







0.33 



0.38 





0.11 



1.92 



0.25 



K 2 . 







4.16 



3.87 





8.51 



6.21 



4.21 



H 2 . 













1.83 



6.49 



5.55 



H 2 + 













4.88 







P 2 B . 







0.22 



0.48 











C0 2 . 







0.14 



0.16 











Sources of the Materials Analyzed 



1. Material resembling greensand from north end of Gay Head section. Analysis made 

 in the laboratory of the U. S. Geological Survey and reported to Professor N. S. Shaler by 

 F. W. Clarke, Seventh Ann. Rept. U. S. Geol. Survey p. 360, 1888. 



2. Same as 1. Both 1 and 2 were partial analyses. 



