540 



r. G. CLAPP GLACIAL PERIOD IN NEAV ENGLAND 



shoving was produced by the Wisconsin ice-sheet. That the Augusta clay is 

 marine is proved'by shells found in it by C. T. Jackson* (column 19, pages 

 530-523). To the argument that the folding may have been produced 

 by a merely local readvance, the ansAver can be made («) that the clay in 

 the Augusta sections represents the marine clay which was deposited when 

 the valley ice-front stood at least as far north as Waterville, and (&) that 

 a local ice-advance after the deposition of a considerable thickness of 

 marine clay would presumably not have exerted so great a power of fold- 

 ing and erosion as took place at Augusta. The general upper level of the 

 clay at Augusta is 200 to 220 feet above tide. Along the electric car 

 line 1 to 2 miles west of that city, however, is a rather flat-tojjped hill, 

 where clay similar to that in the valley rises alcove 300 feet. As this 

 exposure was not examined on foot, no definite statement can he made 

 regarding it, but either (a) this must be a still older clay than the ordi- 

 nary "high-level" clay, or (h) it must have reached its greater altitude 

 through ice-shoving. 



IflGURE 5. 



-Section of Till (Wisconsin) resting on stratified Sand and Clay, near 

 Haierhill, Massachusetts. 



A, fine sand, interstratifiec] witli thin layers of c!aj', worked in a brick-yard one-half 

 mile east ; B, clayey, sandy till, containing boulders up to two feet in diameter ; C, 

 ashes, artificial filling. 



About a mile east of Haverhill, Massachusetts, on the road to Grove- 

 land, is an exposure, part of which is illustrated in plate 57, figure 1. 

 The upper bouldery and gravelly till rests on stratified sand and cla}^, and 

 a fcAV feet distant, where the material is more claye}', it is much con- 

 torted, as if by overriding ice (see figure 5). 



On the western slope of Munjoy hill, Portland, back of the car-barn, is 

 a section which shows over 10 feet of Montauk till overlain by 3 to 5 feet 

 of stratified and crumpled sand and clay, which are in turn overlain by 

 12 to 20 feet of gravel (see figure 6). It is possible that the upper 3 feet 

 of the latter, which is strewn with large boulders, may represent Wiscon- 

 sin till. 



A mild type of fold in clay might be produced by the melting away of 

 buried blocks of ice. It is difficult to imagine how an overturned fold 



* Third annual report on the geology of the state of'Maine, 1839, p, 35. 



