320 MYRON L. FULLER 



the evidence naturally leads to the conclusion that the over- 

 lying oxidized till evidently derived from it was the result of the 

 re-working of the soft decomposed material by the first ice 

 advance, in which case it is probable that it should be correlated 

 with the Kansan or pre-Kansan glacial deposits of the central 

 portion of the country. If, on the other hand, the rock decay is 

 considered as of interglacial origin it constitutes of itself an evi- 

 dence of a long interglacial period. This last supposition, how- 

 ever, cannot be maintained, for the rock weathering is far too 

 extensive, reaching downward as it does to a depth of some feet, 

 to have been brought about in interglacial times. 



An alternative supposition which naturally suggests itself is 

 that the oxidized till may after all be considered as of Wiscon- 

 sin age, and as representing the re-working of the pre-Pleistocene 

 decomposed rock material which had somehow been preserved 

 from the erosive action of the earlier invasions. In answer to 

 this it may be urged that, while the actual erosive power of the 

 earlier advance was comparatively slight, it is almost impossible 

 to conceive of an ice sheet so weak that at a point more than 

 fifty miles from its margin it passed over soft decomposed rock 

 material without re-working it in any degree, especially as till 

 deposits of the corresponding advance occur along the outer 

 margin at Nantucket sixty miles further south. A further and 

 apparently fatal objection to the consideration of the oxidized 

 till as of Wisconsin age lies in the fact that, in the re-working of 

 the previously decayed rock and soil by a sheet known to be spec- 

 ially characterized by numerous foreign fragments, there would 

 at least be a gradual transition between the highly oxidized and 

 the ordinary type of till. In reality, however, the contact is so 

 sharp that the breadth of a hand will usually, and sometimes 

 more than cover it. 



INTERVALE PARK EXPOSURE, BROCKTON 



At the time of the laying out and leveling of the tract of 

 land known as Intervale Park, about a mile west of the Center 

 street locality, a number of good sections of till were transiently 



