F. G. Clapp — Clay of Probable Cretaceous Age. 183 



Art. XVI. — Clay of Probable Cretaceous Age at Boston, 

 Massachusetts* • by Frederick G. Clapp. 



Discovery of the deposit. — During the past few years a 

 great many deep borings bave been made in Boston by the 

 Boston Transit Commission. These have been studied in 

 detail by Professor Crosby ,f who has suggested the probable 

 pre-Pleistocene age of clays in certain wells situated elsewhere 

 in Boston. In 1906 the present writer had occasion to exam- 

 ine some samples of recent borings in connection with his 

 study of Pleistocene succession, and a number of samples of 

 probable pre-Pleistocene deposits were seen. Generally the 

 Transit Commission borings have not been sunk over 20 to 60 

 feet in depth ; they penetrate various types of glacial drift, 

 and commonly end in "hardpan", which is nearly always till. 

 Sometimes they pass through a few feet of stratified blue clay, 

 which, judging from its structure and relations, is Glacial or 

 inter-Glacial in age. The underlying bed-rock of the region 

 consists of Carboniferous slate and conglomerate, which are 

 seldom reached by the Transit Commission borings, but when 

 found are nearly everywhere overlain directly by till. 



Description of deposit. — No deposits between Carboniferous 

 and Pleistocene in age were found until July, 1905, when a 

 boring made at the Ames Building, on Washington at the 

 head of State street, started at an elevation of 33 feet above 

 mean tide,, and was sunk tp the unusual depth of 228 feet. A 

 previous test here had reported bed-rock at a depth of 77 feet, 

 directly underneath the drift. Not being satisfied with the 

 original report, the engineers decided to make a new test, with 

 the result that in the 228-foot boring the following strata were 

 penetrated : 



Record of boring at Ames Building, Boston. 



Thickness Depth 



(feet) (feet) 



10. Coarse sand and gravel 17 IV 



9. Sand 1 18 



8. Gravel and sand 5 23 



7. Coarse gravel and white clay 3 26 



6. Stony sand, gravel and clay with much 



water (very hard) 16 42 



5. Blue clay 18 60 



4. Fine sand .. 5 65 



3. Clay, sand, and gravel, with water (till) 12 77 



2. Hard dry nearly white clay, with bowlders 136 213 



1. Slate (Carboniferous) 15 228 



* Published by permission of the Director of the U. S. Geological Survey. 



f W. O. Crosby : A study of the geology of the Charles River estuary and 

 the formation of Boston Harbor. In Report of the Committee on Charles 

 River Dam, Boston, 1903, pp. 345-369. 



