•440 A. W. GRABAU PALEOZOIC DELTA DEPOSITS OF NORTH AMERICA 



thing is suggested by the fact that the fossils in the basal portion of the 

 red beds, where they overlap the Bald Eagle or rest on its marine equiva- 

 lent, are of uppermost Maysville types. 



An initial uplift of the old land of Appalachia apparently caused an 

 augmentation of river work, so that instead of fine sands and muds 

 coarser sands and pebbles were brought to the seashore by the rivers and 

 these built up into a delta, a large part of which was of subaerial extent. 

 By the end of the time occupied in the formation of this delta — that is, 

 the Bald Eagle — which was completed toward the end of the Lorraine 

 epoch, the seashore of this region had been pushed northwestward prob- 

 ably to the region of Buffalo and southward to near the Maryland bor- 

 der, while northward it probably lay to the north of the present Adiron- 

 dacks, then practically non-existent. That over parts of this delta con- 

 ditions of semiaridity may have at times existed is suggested by the oc- 

 currence of red sand and clay layers at one or more levels in the Bald 

 Eagle, but on the whole there seems to have been a sufficient amount of 

 moisture to prevent general oxidation, or at any rate there were stream 

 and wind work enough to wear the quartz fragments into sand and re- 

 move other mineral particles which by oxidation and dehydration would 

 essentially produce red beds. 



It is difficult if not impossible to conceive of conditions which would 

 bring about such deposition under the present arrangement of moisture- 

 bearing winds. If we conceive of a moderately high, semi-mountainous 

 land on the eastern border of the present North American continent, 

 such as must have existed to furnish all the clastic material piled up in 

 the early Paleozoic formations, and if Ave further postulate a shallow, but 

 extensive sea lying to the west of this, as is indicated by the widespread 

 deposits of marine Ordovicics, we have, with our present westerly winds 

 an admirable arrangement for extensive rainfall on the western slope of 

 such mountains, but such extensive rainfall would be accompanied by 

 much vegetation, especially if, as seems likely from the nature of the 

 Ordovicic fauna, the sea was a warm one. Such vegetation would, of 

 course, be prohibitive of much torrential or eolian deposition, for the 

 mantle of vegetation would protect the underlying rock from erosion 

 except locally. Such conditions now exist on the western slopes of the 

 Coast Eanges of Oregon, which face the ocean and run at right angles to 

 the direction of the westerly winds. Here the rainfall exceeds 100 inches 

 a year. 59 The eastern side of these mountains, on the other hand, are 

 much drier except where local features are operative. "The great height 



69 Isaiah Bowman : Forest physiography, p. 117. 



