296 NATURAL SCIENCE. April. 



Stability of Conditions Indicated by the Accumulation of 

 Great Thicknesses of Sediment over certain Areas. 

 The accumulation of great thicknesses of sediments extending over 

 milHons of square miles, such as took place in Cretaceous and Tertiary 

 times over what is now the vv^estern half of the North American 

 Continent, points to an extraordinary constancy of conditions over a 

 vast period of time. Greater than this, perhaps, is the record of the 

 earth's history within the Appalachian chain at an earlier period 

 ending with the close of the Palaeozoic, We will, however, for the 

 nonce, confine ourselves to the first-named area, in which are 

 situated the Rockies, the Cascades and Coast Ranges, extending with 

 their analogues through 60 degrees of latitude from Central America 

 to Alaska. It is next to impossible with our present lack of informa- 

 tion, though the geology of the North American continent has pro- 

 gressed with rapid strides, to sketch out the disposition of land and 

 sea which endured through the Cretaceous and Tertiary. 



It is highly probable, however, that the old Laurentian areas of 

 Canada and the eastward areas of the United States, with other land 

 stretching into the Atlantic, provided at least part of the sediment. 

 It is pointed out that the deposition of sediment, leaving out of 

 account matters in solution, takes place over a smaller area than that 

 of the land from which it is derived. This would seem to indicate 

 that though general conditions of stability of land-areas obtained, 

 fluctuations of distribution occurred throughout the history of these 

 periods in North America. Land to the westward, an extension of 

 the Asiatic continent eastward, may very likely have sent important 

 contributions towards the making of the future land. But, as I have 

 said, these are speculations which, if we had all the complicated facts 

 before us instead of buried beneath the sea, might not yield satisfac- 

 torily to imaginative reconstruction, much less to minds in the 

 position that ours are now. 



It is highly probable that many fluctuations of level occurred, 

 and that sediments were raised above the level of the sea and again 

 redistributed. Still, on the whole the locus was the same, and 

 so in time the sea-bed got built up, until the internal forces of the 

 earth, reacting upon this varied sedimentary load, began their role of 

 mountain- and land-building, and the estabUshment of the western 

 area of the North American continent. 



In like manner, we might trace the growth of the European con- 

 tinent as it now exists, together with that of a large part of Asia, 

 where the record of the rocks tells the tale of long-continued periods of 

 sedimentation, culminating in the upheaval of the Alps, the Cauca- 

 sians, the ranges of Turco-Persia, and the Himalayas. 



The story might be extended to South America and Australasia, 

 but for the purpose of illustration the two examples given are 

 sufficient. 



The later rocks of the series more or less represent land condi- 



