NO. 4 PHYSIOGRAPHY OF ROCKY MOUNTAINS- — LEE Z7 



gression seems to have been a relatively small one. On the principle 

 of wide uniformity of action, apparently necessary if diastrophic 

 principles are to be of material use in long-distance correlation, a 

 similar advance of the sea over the other continents should be found. 

 The great development of the Jurassic system in Europe shows that 

 large parts of that continent were under water during much of the 

 period, but the greatest submergence seems to have been in late 

 Jurassic time. E. W. Berry, who has recently reviewed the conditions 

 in Europe during this time, is of the opinion ' that the transgression 

 of the Jurassic sea, which commenced at about the close of the middle 

 Jurassic, reached its maximum extent in the Upper Jurassic (Kime- 

 ridgian stage), and that its subsequent withdrawal, which marks the 

 close of the Jurassic period, was probably contemporaneous with the 

 similar withdrawal of the Jurassic sea in western North America, 

 and both series of events may have been the result of a common 

 cause. In other parts of the world relatively small areas comparable 

 in size with the Jurassic areas of North America were submerged 

 also in late Jurassic time. (See fig. 341 of Haug's textbook.) 



Also, attention may be called to the fact that the Jurassic seems to 

 have been a period of general continental stability. There were land 

 movements in places and some of these movements attained consid- 

 erable importance, but the continents were chiefly above sea-level 

 and subjected to erosion throughout the period. The Jurassic has 

 been termed a period of repose in contrast to the Cretaceous, which 

 as a whole was a period of diastrophic activity. If the continents 

 were really as stable as they seem to have been, the marine invasion 

 may have been due to a rise of sea-level. It seems reasonable to 

 attribute this rise to the discharge into the basins of sediments 

 derived from long erosion of the lands. It has been shown that the 

 volume of land now above sea-level is sufficient to raise the level of 

 the sea 650 feet. If the Jurassic was a period of world-wide con- 

 tinental repose, we may reasonably attribute the submergence of low- 

 lying areas to a general rise of sea-level. Also, we may reasonably 

 assume that aside from the effect of local warping of the surface, 

 maximum submergence at widely separated localities denotes equiva- 

 lency in time. 



DRAINAGE OF JURASSIC. SEA 



Following this hypothesis still further, if the Jurassic submergence 

 was due to transfer of rock waste from the land to the sea, with 

 resulting rise of sea-level, what was the cause of the withdrawal of 



1 Berry, E. W., Personal communication. 



