536 r. G. CLAPP GLACIAL PERIOD IN NEW ENGLAND 



In most borings the depth of oxidation is 5 to 15 feet, but a few records 

 have been seen in which it is over 20 feet. ISTo two borings give exactly 

 the same section, and to show the variations in a short distance the fol- 

 lowing is given. It is situated midway between Beach and Essex streets 

 on Atlantic avenue. 



Section of Boring at Boston 



Material Feet 



7. Filling 9 



6. Fine sand, mud 4 



5. Hard yellowclay, little sand 5 



4. Little clay, sand, coarse gravel 4 



3. Hard blue clay, sand 11 



2. Hard blue clay. 10 



1. Clay, sand, gravel, hard 8 



Total 51 



The great number of borings at Boston makes it possible to trace out 

 with some degree of accuracy the courses of valleys which were deeply 

 eroded in the clay, and subsequently buried by sand and other deposits. 

 As stated by Crosby, the maximum depth of valleys in the blue clay is 50 

 feet. 



"That the erosion of the clay producing all the depressions now occupied by 

 the inner harbor was subaerial and not marine, fluvial and not tidal, and that 

 It extended over a long time, are indicated by the superficial yellowing of the 

 clay through the oxidizing influence of the atmosphere." 



Crosby, hoAvever, believed the clay to be of Wisconsin age. 



Evidence that the dnimlins are older than the principal clay in the 

 borings was found on Hanover street, where the "toe" of Copps Hill 

 drumlin descends to — 30 feet and the clay rests on top of it. Nearly 

 everywhere the clay is underlain by a stony hard-pan believed to be 

 Montauk, and in man)^ places the oxidized upper surface of the clay is 

 overlain by a hard gravelly deposit resembling Wisconsin till (pages 

 546-547). The deep oxidation of the clay — as deep as the deepest oxida- 

 tion of the underlying till where it is exposed — and the correspondence of 

 the clay oxidation with an unconformity which must have taken thou- 

 sands of years to form, being later covered with sands, gravels, and silts, 

 indicate the interglacial age of this clay with a strong degree of proba- 

 bility. 



3. Occurrence of overlying till and morainal deposits. — Good sections 

 have been seen of till overlymg clay at a number of places in northeastern 

 New England. One of the best examples ,is at the works of the New 

 England Brick compan}^, 2 miles sotitli of Exeter, New Hampshire, where 



