6o6 FRANCIS PARKER SHEPARD 



Such a range might be considered as pre-Cambriari. If deposition 

 covers an old range, it may remain undiscovered until drill cores cut 

 through the overlying sedimentaries. The buried granite ridges of 

 the Mid-Continent oil fields are examples of such occurrences. 



2. Rejuvenation unrecorded. — Most of the fairly recent mountain 

 ranges show evidence of rejuvenation following their first uplifts. 

 Such rejuvenation probably indicates a shortening of the earth's 

 crust and should be considered in estimating the importance of dias- 

 trophic movements during the history of geology. It is only reason- 

 able to suppose that the earlier ranges were also rejuvenated. Some 

 of them are still ranges of considerable size and show undoubted 

 rejuvenation. Usually the records of such renewed deformation 

 are lacking. It is not unreasonable to suppose that such deforma- 

 tions may have helped make up for the deficiency of diastrophism 

 during certain periods. For example, during the Cambrian where 

 the diastrophic record is lacking, there may have been considerable 

 deformation in the old pre-Cambrian ranges. It is even not improb- 

 able to suppose that what we consider to be pre-Cambrian folding is 

 actually in some cases of early Paleozoic age with the disturbance 

 involving only older sediments, either because of the local absence 

 of the more recent sediments or because the Paleozoic present has 

 been metamorphosed. 



3. Diastrophic records submerged. — Since there is constant chang- 

 ing of the distribution of the lands, it is not unreasonable to suppose 

 that the roots of old mountain ranges may be at present submerged 

 beneath the sea. The old land of Appalachia is at least so buried in 

 part. If this land supplied sediment to the Appalachian trough 

 through much of the Paleozoic, it is likely that it was a mountainous 

 country. The Carboniferous conglomerates of southeastern New 

 England probably came from a land to the east of the present coast 

 line. The thickness and coarseness of these conglomerates indicates 

 without much question that they came from mountain ranges. 

 Such sedimentary records have been neglected in considering the 

 times of diastrophic movements, but they are reKable evidence of 

 orogeny. 



4. Sub-oceanic diastrophism. — A common fallacy among geolo- 

 gists is to consider that most of the orogenic diastrophism has 



