. Bulletin of the Geological Society of America. Geology. FOSSILIFEROUS MARINE CLAYS 541 like that described on page 539 could be so produced, however. Tn several cases the occurrence of folds in which the inclination of the strata is toward the south seem to indicate a lateral pressure from the north. If lateral pressure was the cause, it can hardh^ have been due to anything but ice. The general assumption in the past has been that such instances were due to local readvances of the ice. If, however, the clay at Haverhill, Augusta, Portland, and elscAvhere is of the same age as that in Portlan
. Bulletin of the Geological Society of America. Geology. FOSSILIFEROUS MARINE CLAYS 541 like that described on page 539 could be so produced, however. Tn several cases the occurrence of folds in which the inclination of the strata is toward the south seem to indicate a lateral pressure from the north. If lateral pressure was the cause, it can hardh^ have been due to anything but ice. The general assumption in the past has been that such instances were due to local readvances of the ice. If, however, the clay at Haverhill, Augusta, Portland, and elscAvhere is of the same age as that in Portland and Boston harbors, as its relations with the underlying clay and overly- ing gravels render probable, the evidence afforded by the subaerial erosion and oxidation of the clay surface must be taken into account as intlicat- T\ " â -â â ' . ".ââvâ^ii j2_. -SF*- Figure 6.âSection at Munjoy Bill, Portland, Maine. Showing contorted clay and its relations to underlying till and overlying gravels. A, hard, blue till, Montauk ; B, stratified sand and clay, unconformable on A; C, coarse, stratified gravel, resting unconformably on B; D, heterogeneous, boulder-filled and boulder-strewn gravel, possibly representative of Wisconsin till. ing a lapse of thousands of years between the deposition of the c\&y and its folding. On the basis of this kind of evidence it seems probable that ice has covered the greater part of the surface of the New England clays. The absence of folding and of deposits of till over considerable areas is not evidence to the contrary, for in Alaska, where living glaciers are seen, they have Ijeen observed by P. E. Wright and otliers to be at pre,~ent retreating in places over clayey deposits with almost no deposition of till and no perceptible erosion or folding. Absence of erosion may per- haps be due to the presence of water above the deposits during tlie ice- advance. 5. Eeworked upper part of some clays.âIn most of the clay pits which have
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