CONTINENTAL RELATIONS AS REVEALED BY DEPOSITS. 349 



nent, brought about by seaward tilting and accompanied by landward 

 elevation, which produced increased activity in the streams. The weath- 

 ered materials of the surface rocks which had become disintegrated to 

 great depths on account of the relative]}'' low elevation of the land in the 

 previous period were carried seaward, thick beds of sands and clays often 

 characterized by large amounts of arkose being formed. Several epochs 

 of elevation and depression with variations in the angle and direction of 

 tilting doubtless took place during the period, with the result that the 

 land must have been considerably planed down prior to the opening of 

 the upper Cretaceous. 



The upper Cretaceous was probably ushered in by a general depres- 

 sion of the area draining to the Atlantic border, which must have dimin- 

 ished the power of the streams and at the same time decreased the supply 

 of sediment. This was probably also accompanied by some depression 

 of the sea-floor as well ; yet from the descriptions which have been given 

 in the previous pages regarding the character, distribution, and relations 

 of the sediments it is evident that the continental conditions could hardly 

 have been constant throughout the period of Upper Cretaceous deposi- 

 tion. Oscillations of greater or less moment, accompanied by increased 

 activity of the streams, must have taken place from time to time, but 

 these changes were not identical or synchronous throughout all portions 

 of the northern Atlantic slope. At the same time many of the minor 

 changes may find their explanation in the direction of transport brought 

 about by variations in the oceanic currents adjacent to the continent 

 border. Such an explanation is, however, wholly inadequate to account 

 for the great deposits of sand in the upper Matawan of northern New 

 Jersey, the lower Monmouth of central and southern New Jersey, Dela- 

 ware, and Maryland, and the upper Monmouth of northern New Jersey 

 and the Delaware peninsula. The largely increased deposits of coarse 

 materials at these epochs over the wide areas indicated could only have 

 been brought about by changes upon the adjacent land surface. 



The close of the upper Cretaceous witnessed the general elevation of 

 the entire area, the gradual stripping off of the Cretaceous cover, and the 

 superimposition of the consequent streams upon the underlying rocks 

 to which, under varying conditions, they have been continuing to adjust 

 themselves during subsequent periods. 



SUBSEQUENT STRUCTURAL AND CHEMICAL CHANGES IN THE STRATA. 



The interpretation of the sedimentary record would hardly be com- 

 plete without reference to the changes, both structural and chemical, 

 which have taken place in the strata subsequent to their deposition. 

 The various oscillations of the northern Atlantic Coastal plain have pro- 



