GEOLOGICAL CHARACTERISTICS OF THE VALLEY REGION 217 



are to a greater or less extent developed, and these partially obstruct the 

 valleys (pages 211, 214, 216). Off cape Hatteras, dredgings bring up 

 quantities of old Miocene water-worn shells mixed with modern species. 

 Miocene beds occur in Maryland and New Jersey, while they have been 

 removed from Long island, which is surmounted by drift ; but fragments 

 of Miocene beds recur in Marthas Vineyard, and have been recovered by 

 dredgings from depths of 35 to 70 fathoms, off the Georges shoals, south of 

 the gulf of Maine. The same have been found on the Banquereau, south- 

 east of cape Breton, adjacent to the Laurentian channel. Again Tertiary 

 fossils have been obtained from the great bank of Newfoundland (lati- 

 tude 44 degrees 30 minutes, longitude 50 degrees 15 minutes). While 

 the drowned plains off Maryland and New Jerse}^ are covered by sands, 

 these do not appear in the Hudson channel, as it incises the continental 

 shelf, for here is found a fine blue clay. It thus appears that the com- 

 pletion of the valleys of the submarine coastal plain has been since the 

 old Miocene period, and their origin, due to atmospheric erosion during 

 a period of land elevation, may not be questioned. The great Lauren- 

 tian valley doubtless owes part of its origin to a much earlier date, but 

 while it is excavated out of all the formations represented since Archsean 

 times, it cuts through Carboniferous and Triassic rocks, and consequently 

 is of later date. As has been shown by Professor W J McGee,* the great 

 period of erosion was after the accumulation of Lafayette formation, and 

 these deposits, as the writer has seen, underlie the drift of New Jersey. 

 The Lafayette was accumulated after a long period of Tertiary erosion of 

 this region, and is provisionally regarded as of late Pliocene age. Doctor 

 Dall has shown that some fossiliferous beds beneath the Dismal swamp 

 of Virginia are referable to the Pliocene period. The pre-Lafayette ero- 

 sion gave rise to flattened topography of the old Miocene surface. The 

 formation of the channels of the Coastal plain, or their reopening, was 

 after the Lafayette period, or early Pleistocene epoch, when the fiords of 

 Newfoundland and Nova Scotia were fashioned, but prior to the accu- 

 mulation of the drift or the Columbia formation, both of which kinds 

 of deposits rest on the post-Lafayette topographic surfaces. 



From the continuity of the continental shelf with the coastal plain 

 and the occurrence of similar formations on the outlying banks, one is 

 led to conclude that the plains, whether now above or below sealevel, 

 form one feature, and that the sands, more or less filling the valleys, is 

 only such a feature as would be produced by the shght changes of level 

 that have occurred since the mid-Pleistocene epoch. It is also interest- 

 ing to note that the banks of Newfoundland, which show the same char- 

 acter of submarine plains as in the region south of the drift, are not so 



* The Lafayette. 



