CAPE COD GEOLOGY 



253 



a bed of this gravel about 20 feet thick was exposed in 1915-16 above the beach. 



Its components are subangular and waterworn pebbles or cobbles, the largest 



8 inches in diameter, indicating very strong stream work. Ten feet below the 



contact of this bed with the overlying clay there is dark-purplish felsite, felsite 



breccia, and felsite having flow structure, some of it in angular blocks about a 



foot long. There are also pebbles of gray quartzite, fine red shale, compact 



argillite, schist, lustrous crumpled phyllite like that at Savin Rock south of 



New Haven; granitite, gabbroid, and dioritic rock resembling that on the east 



coast near Boston ; and waterworn pebbles of a red conglomerate that resembles 



some forms of the Roxbury conglomerate found near Boston. In the bluffs 



north of the clay pounds or near this horizon there were seen also angular boulders 



(one of felsite) nearly 3 feet long. South of the clay pounds the section changes 



as it rises on a gentle northward dip to a series of alternating beds of gravel 



and sand. Farther south it is difficult to trace bed to bed because of the talus. 



Among the coarse fragments found in the gravel about 10 feet below the base 



of the clay was a quadrangular piece of Devonian fossiliferous semi-quartzite 



about 6§ inches long, filled with fossil casts. Dr. Ulrich, who examined these 



casts, stated that the fossils consist of brachiopods, pelecypods, and trilobites, 



all poorly preserved. He furnished the following list : 



Dalmanella sp. Cf. D. planoconwxa 



Schizophoria sp. 



Modiomorpha sp. 



Homolonotus; fragments of a trilobite suggesting this genus. 



The horizon at which this fragment was found is regarded by Ulrich as 

 Lower Devonian. The rock is made up of fine grains of light blue quartz, which 

 weathers yellowish. At nearly the same horizon in the gravel but farther south 

 and higher up in the cliff on account of the rise of the beds in a fold, a slabby 

 fragment containing small patches of clay was found. These patches look like 

 fossil shells. 



In the same beds, near the top of the cliff, at the southern limit of the 

 government lot, I found a flatfish finely stratified greenish-hued quartzite show- 

 ing faint ripple marks and carrying on the flat side three impressions having 

 a hyolithoid outline. One of these impressions was distinctly marked with 

 transverse lines of growth. Dr. Walcott identified this material as a species of 

 Hyolithes, probably but not certainly Cambrian. 



In a thin patch of lag gravel on top of a bed of fine sand (Jacob?) just north 

 of the Weather Bureau Station, I found a weathered specimen of quartzite 

 showing the parallel closely set ribs of Scolithus, a form found from the Lower 



