53 BULLETIN" OF THE NATURAL HISTORY SOCIETY. 



Williams' and Dana's estimates were based lars-elv 

 on observations in the eastern United States ; Wincheirs, 

 on studies in the north-central States ; Walcott appears 

 to have given more weight to the evidence obtained in 

 the western States, where the Mesozoic and Cainozoic 

 rocks prevail. I should be inclined to think his propor- 

 tions nearer the truth, as thev accord better with Euro- 

 pean estimates of the comparative lengtli of the several 

 great divisions of o;eolo£!:ical time. 



Walcott has gone further and given us an estimate 

 by years of these several great divisions of time, allowing 

 nearly one and a half millions of years to each unit of 

 the time ratios. Taking his estimate we may say that 

 for ten millions of years, during which vast changes in 

 the life history and physical conditions of the globe took 

 place, the record here is a complete blank. During 

 most of the time it probably was for this region a period 

 of continental elevation, when the rivers cut deep canons 

 and valley's into the earth's crust, and when the ocean 

 margin was far off to the south, along the outer banks 

 which exist on the Atlantic coast, from Nantucket to 

 Sable Island. This was the period of the carving out 

 of valleys bj' flood and storm in preparation for the needs 

 of the St. John at a later time.^ 



* The Continental border at this period in New England is indicated by beds of 

 sand, gravel and clay of considerable extent and thickness in Long Island, Martha's 

 Vineyard, Nantucket, and the shoals eastward of this island; and though thinner 

 deposits in shallower estuaries and lakes were no doubt formed contemporaneously 

 further to the north, they have been comparatively thin and have been almost 

 entirely swept away by subsequent sub-aerial erosion. Small patches of sediments 

 of the Cretaceous period have been found in Blassachusetts, of the Tertiary in 

 Vermont, and again of the Cretaceous in Wisconsin and Minnesota, on the borders 

 of this Continental area. But on the whole it would be safe to assume that during 

 the long Secondary and Tertiary ages (Mesozoic and Cainozoic) that elapsed after 

 the Trias and before the Glacial period. New England and all Eastern Canada was 

 above the sea, and at times of greater extent and height than now. 



