534 F. G. CLAPP GLACIAL PERIOD IN NEW ENGLAND 



vauced by some, that the differences in deptli of weathering were due to 

 different conditions of moisture, porosit}'- or climate in different localities. 

 In all cases, however, the differences could be accounted for by (a) 

 the peculiar situation of tlie deposit — that is, where it might be a part 

 of the "low-level" or AVisconsin deposit, or ( 5 ) the possibility of part of 

 the surface having been removed by erosion since the weathering took 

 place. Oxidation of 5 to 12 feet in the clays has been noted by Crosby 

 in his studies of the materials found in borings at Boston. 



2. Oxidation of buried clay surfaces which were formed by subaerial 

 erosion. — Evid-ence of an elevation and a subsidence since the deposition 

 of the principal clay deposit is found in a series of borings made in 1905 

 at Vaughans bridge over Fore river at Portland. In making tests here 

 two rows of 13 borings each were put down across the river between Port- 

 land and South Portland. The borings were sunk to bed-rock, which 

 dips rather regularly from -15 feet below mean Iom^ water on the Portland 

 side to 110 feet below on the South Portland side. A typical record is 

 as follows, beginning at low-water level : 



Boriii'l for Vundliaiis Brich/c. PoiiJaiid. Maine 



Material Feet 



Water 11.9 



5. Soft black silt 21.4 



4. Soft black sand and peat ' 21 .0 



3. Very soft blue clay, with silt 52.8 



2. Coarse gravel and sand, bard 2.4 



1. Rock. 



Total : 109.5 



Samples of these deposits were on exhibition at City Hall, and were 

 examined by the writer. jSTumber 5 is a brownish gray clay, rather silty 

 and similar to much of the clay, found 20 to 40 feet above tide in the 

 vicinity of Portland. Number 4 is in some cases a nearly pure peat ; in 

 others it is made up largely of sand. It is only found in 10 out of the 

 26 borings, and has a thickness, where mixed with sand, of from 5 to 30 

 feet. Its upper surface rises to within about 30 feet of the present low- 

 water level. Number 3 is a typical blue clay, a little lighter in color 

 than number 5 and resembling some brick-yard clays seen in southwestern 

 Maine. The surface of this deposit rises from — 55 feet at South Port- 

 land to sealevel at Portland. The top of this clay is yellow to the depth 

 of several feet below the overlying deposits. Number 2 is a typical stony 

 till of the Montauk type. 



The descent of the clay from sealevel to 55 feet below, with an oxidized 



