152 N. S. SHALER — EVIDENCES AS TO CHANGE OP SEALEVEL. 



deposits from the surface of the lower lymg lands. To test the matter I 

 resorted to the country lying on the west and south of lake Ontario, 

 where the well preserved Iroquois beach indubitably proves long con- 

 tinued sojourn of the waters at a considerable height above their present 

 level. I found that below the plane of the beach the general surface of 

 the country showed no distinct indications that it had been submerged. 

 In fact, I was unable to find any criteria which would enable me to dis- 

 criminate the areas below and above the ancient sea-margin. It must 

 be believed that where the submergence has endured for a long time a 

 certain amount of sediments w^ould be laid down in the offshore district, 

 and that the period required for the formation of such a beach as that 

 last mentioned should have brought about a considerable accumulation 

 of clay. It seems, however, likely that in a few thousand years of ex- 

 posure such clay deposits would by the down bearing action of the rain- 

 waters be carried down into the earth or washed away into the streams. 

 Thus in the sandy and gravelly areas of southern New England it is here 

 and there the custom to improve the roads by covering their surfaces 

 with glacial and other clays. Experience shows that such a coating, 

 originally several inches in thickness, will in the course of five j^ears 

 completely disappear. Even where marine deposits contain fossils the 

 removal of the clay element Avould lead to the rapid decay of all organic 

 remains. It seems to me that in this way we may account for the dis- 

 appearance of relatively thin offshore deposits made below the plane of 

 ancient sea-margins. 



Criteria indicating lower Seashores. 



s ubmer ged esc a "rpbients. 



The evidence that the shore has been farther to the seaward, that is, 

 at lower levels than at present, is unfortunately of a very obscure nature. 

 Here and there submerged escarpments lying below the plane of wave- 

 action are traceable under conditions which make it likely tliat they are 

 not due to fault-action, but are indeed the products of wave-work. Here 

 and there steepenings of the slope on the surface of the continental shelf 

 may afibrd grounds for inferences of some value. 



FLOODED VALLEYS. 



Thus far the only proof of value, and that happily of much w^eight, is 

 afforded by the flooded valleys which intersect, as we shall see hereafter, 

 the larger part of continental coastlines. It seems to me unquestionable 

 that where a coast exhibits a system of valleys affording drainage to large 

 rivers, the basins of which have been the seat of abundant and recent 



