310 



CAPE COD GEOLOGY 



of gravel underlain by a fine yellow sand. A few feet farther east a lignitic 

 Cretaceous bed rises about 6 feet above the limit of marine action. This bed 

 discloses the following section, the layers being named from above downward: 



Cretaceous beds on Nonamesset 



Black lignitic clay containing some lignite. 



Pinkish gray clay containing a sandy iron-stained layer that furnishes the ferruginous 



concretions seen on the beach. 

 Quartz gravel. 

 Light yellow sand. 

 Lignite underlain by clay imperfectly exposed. 



Miocene Greensand 



About two rods east of this bed is a Pleistocene section, which is underlain 

 by a layer of yellowish greensand, a mixture of quartz grains fairly well rounded, 

 and a few black, rounded nodules such as are found in the Miocene greensand 

 bed on Gay Head, probably the altered casts of foraminifers. Still farther east 

 the nodule-bearing Cretaceous clays reappear at the edge of the beach. 



Pleistocene Sections 



Between the points just mentioned the Pleistocene section exhibits various 

 features in different thin deposits. 



Pleistocene section on Nonamesset Island _, , 



beet 



Bouldery surface drift 1-3 



Uncomformity 



Fine, light sand 4 



Zone of angular blocks of granite, etc 1-4 



Till (?) A gravelly unstratified clay 4 



Gray, streaked sand, which grades downward into ferruginous 



red sand • 3-4 



Coarse glacial gravel 6+ 



These glacial deposits resemble in character and succession the older Pleis- 

 tocene beds just above the Cretaceous and Tertiary beds in the Gay Head cliffs. 

 They include deposits formed at stages as late as the second ice advance here 

 recognized. The beds are tilted, and the surficial bouldery drift of the Wis- 

 consin stage is only a veneer over a mass of older Pleistocene deposits. 



Most of the boulders on Nonamesset are of granite-gneiss, some of which 

 contain traces of banded schist. 



Several years ago boulders were struck at a depth of 80 feet in wells bored 



