198 H. L. FAIRCHILD POST-GLACIAL UPLIFT OF N. E. AMERICA 



The greater thickness of the broad valley deposits is usually massive 

 clay or silt and is capped by sand. The deep clays of the Hudson, Cham- 

 plain, Connecticut, and other New England valleys are well known and 

 are often 100 or 200 feet in thickness. W. A. Johnston says that in the 

 lower part of the Ottawa Yalley the clays have a vertical range of 600 

 feet (48, page 20). The occurrence of finely laminated clay and silt is 

 proof of a higher surface of relatively quiet water. The depth is variable, 

 according to variant combination of factors ; but the least depth noted by 

 the writer is at Bradford, Vermont, where, in the valleys of Waits Eiver 

 and Mink Brook, the clay reaches up to within 60 feet of the theoretic 

 and the measured water surface. At Ottawa City the land uplift is about 

 700 feet and the clays lie at 600 feet. 



In his monograph on the glacial gravels of Maine, previously noted, 

 George H. Stone makes special mention of the clays. Like the Hudson 

 and the Connecticut, the deep valleys of Maine afford good examples of 

 the fiord or estuarine character. And as the valleys open directly south- 

 ward to the sea there can be no doubt of the nature of the flooding. Con- 

 cerning the valley plains. Stone writes : 



"The hypothesis that there was a greater elevation of the interior tlian of 

 the coast region of Maine helps clarifj^ some heretofore very doubtful points 

 of interpretation. At elevations extending from 350 to 450 or 500 feet are 

 plains of valley sediments up to 5 miles in breadth, and in a few cases they 

 are somewhat wider. If these great sheets are valley drift, they demand very 

 large rivers. But if they are in large part marine beds — that is, fluviatile 

 deltas formed offshore in bays or fiords — we do not need so large streams to 

 account for them" (page 488). 



"Below Moscow and Bingham the sedimentary plain of the Kennebec is 

 from 1 to 6 or 7 miles wide" (page 489). 



Concerning the clays. Stone says : 



". . . For instance, a nearly continuous sheet of clay extends from the 

 sea up the valleys of the Kennebec and Sandy rivers to a height of 450 feet or 

 more" (page 56). 



Stone's map of the marine clays (his plate 2) makes the clay extend 

 up the Penobscot Valley to the isobase of 500 feet uplift and up the Ken- 

 nebec Valley to the 6 50 -foot line. This implies a depth of 200 feet of 

 water over the northern Kennebec clays. 



The mistake in regarding the wide silt plains of the broad lower valleys 

 as indicating the earliest water planes was probably due to mental pre- 

 possession of the theory of small land uplift or none at all. Like other 

 features in ilie valleys, these plains ]iave no satisfactory ex]:>laiiation 

 except by deep submergence. 



