314 /. Bowman — Atlantic Preglacial Deposits. 



of Scituate Harbor. They are represented on the Duxbury 

 Sheet, U. S. G. S., as the eroded edges of drumlin-shaped 

 hills, from 20 to 75 feet high and with major axes trending 

 MW. The accompanying sketch (fig. 1) of a part of Third Cliff 

 depicts the chief features referred to in the following descrip- 

 tion. 



Lithologic and Structural Features. 



Preglacial Seines. (1) Basal clays. — The basal member 

 of the Third Cliff section is a layer of clay having the 

 light yellow color of terra cotta. The top of the layer is 

 about at the level of high tide, and an excavation of several 

 feet failed to reach the bottom. It lies in a nearly horizontal 

 position, with slight dip to eastward. It is extremely unctu- 

 ous when wet and resists wave action to such a degree that 



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BOULDERV , o , 'BEACl 



Fig. 1. Topograph}' and structural relations of part of Third Cliff. 

 Heavy continuous lines represent observed structures. Heavy dotted lines 

 represent inferred structures. Horizontal scale = 175 feet to the inch. 

 Vertical scale = 130 feet to the inch. 



the height of the steeply-sloping bowlder-strewn beach (fig. 1) 

 is determined by its upper surface. Within the body of the 

 deposit the clay is very pure, but towards the top becomes 

 more sandy, containing round inclusions of yellow sands up to 

 a centimeter in diameter. Lamination appears near the upper 

 surface, at first faintly and then more strongly marked, chang- 

 ing finally into cross-bedded structure, although the bulk of 

 the material is still clay. An 18-inch deposit of alternating 

 yellow sands and clays, of several inches thickness each, com- 

 pletes this lowest member of the preglacial series. The 

 entire layer contains muscovite in considerable quantity, and 

 under the microscope shows an occasional grain of glauconite 

 and scattered fragments of sponge spicules, none of which 

 have sufficient character to be identifiable, although one 

 specimen suggested a form of Geodia. 



(2) Yellow and white sands. — A deposit of yellow and 

 white sands lies conformably upon the basal clay, the latter 

 color gaining predominance towards the top. Like the clays 



