184 JF. G. Clapp — Clay of Probable Cretaceous Age. 



According to the system of the Transit Commission, sam- 

 ples were collected from the boring at intervals of every few 

 feet, and are preserved at the office of the Commission, where 

 they were seen by the writer through the courtesy of Mr. 

 Howard A. Carson, chief engineer. Down to 77 feet from 

 the surface the materials are the ordinary sand, gravel, clay 

 and till of the region, shown by their character to be entirely 

 of Pleistocene age. They are mostly rather wet and yield 

 considerable water. The material below 77 feet is dry, and 

 in a previous boring had been called rock and not entered by 

 the drill. All the samples of this bed were seen by the writer 

 and found to consist mostly of a very fine-grained gray to 

 white clay, which became plastic when wet. It varied from 

 very soft and putty-like to nearly as hard as the underlying 

 slate. The material when examined by Dr. W. T. Schaller of 

 the United States Geological Survey was found to consist of 

 Si0 2 =- 59-18 per cent and (Al a O„Fe s O„P 9 5 ,TiO a ) = 27-11 per 

 cent, thus being a very pure clay. 



Two masses, one consisting of sandstone, the other of fine- 

 grained conglomerate, were found in the clay, and each 

 measured about 1^ feet in thickness. These may be interstrat- 

 ified beds of rock, or, as their relations and character seem to 

 indicate, they may be bowlders. No other foreign matter was 

 found in the clay. Since the surface of the Carboniferous 

 bed-rock buried underneath the city of Boston is very hilly 

 and is eroded into deep river channels, it seems possible that 

 bowlders might become detached from a near-by ledge due to 

 action of currents, and incorporated in the clayey sediments 

 during their deposition. 



Difference from Pleistocene clays. — This clay is important 

 for the reason that it is unlike the general type of clay found 

 at Boston. All the Pleistocene clays of the vicinity are of 

 blue-gray to brown or -buff colors; this clay is light gray to 

 nearly white. The Pleistocene clays contain numerous 

 bowlders and pebbles composed of all lands of rock found in 

 New England, but in this clay only two bowlders have been 

 discovered, and these consist of rock only found in the vicin- 

 ity of Boston, and which forms the bed-rock of the region. 

 The Pleistocene clays are interstratified with glacial deposits : 

 this clay rests on bed-rock and is separated from the overlying 

 Pleistocene clay by a bed of till. This clay is much dryer 

 than the overlying Pleistocene clay. 



Similar clay in other borings. — In a boring at Dock Square, 

 Boston, also made by the Transit Commission, samples of 

 which were examined by the writer, a number of fragments 

 of white clay (No. 2 in the record) were scattered through the 

 brown Pleistocene clay at depths of 23, 30, and 31 feet from 



