42(3 A. W. GRABAU PALEOZOIC DELTA DEPOSITS OF NORTH AMERICA 



on an old land of crystalline character, from the disintegration of which 

 it was apparently derived, but that is hardly a good analogy, since the 

 Potsdam sandstone represents residual quartz most probably reworked 

 during an enormous length of time (the whole Cambric and perhaps a 

 part of Algonkic time) by both wind and water, until all the decom- 

 posable material had been removed before it was finally buried as an 

 Upper Cambric (Lower Ordovicic) sandstone. But during Lorraine 

 time the Adirondacks and the Canadian region had no such accumulated 

 material, as is shown by the fact that pure limestones like the Trenton 

 were forming in the immediate vicinity of the crystallines, and in some 

 cases, as at Kingston Mills, Ontario, 41 and elsewhere, rested directly on 

 the smooth floor of crystalline rock. Indeed, there is good reason for 

 believing that the greater part of the Adirondacks, if not the whole of 

 them, were covered by Trenton limestone and later deposits, and that 

 these were not removed until the end of Siluric time. The Canadian 

 shield likewise seems to have been covered to such a degree that it could 

 hardly have furnished clastic material for such a sandstone. 



If these conclusions are correct, there seems to be no other source than 

 the Appalachian old land for these sandstones, and indeed they or their 

 Xew England extensions must have furnished the sand and mud for the 

 Hudson Eiver elastics throughout, since the Adirondack and Canadian 

 areas permitted the simultaneous deposition of calcareous sediments. 

 This is shown by the fact that around these old land-masses the deposits 

 of the whole lower and middle, as well as part of the Upper Ordovicic, 

 are calcareous, while to the southeast they are replaced by the siliceous 

 deposits forming the Hudson Eiver group. 



If we admit the Appalachian source of the Oswego sands for the east- 

 ern region, we must admit it for western Xew York as well, and, for the 

 same reason, we must connect these sandstones with the Bald Eagle fan. 

 For such a deposit of pure sands calls for a corresponding, though not 

 necessarily, as pure a deposit nearer to the source. It is also logical to 

 assume that such a deposit should become coarser and thicker as we ap- 

 proach the source of the material. There is no sandstone or conglom- 

 erate in the Appalachians which fits these requirements and is at the 

 same time of the corresponding age except the Bald Eagle. Even if we 

 regard this formation as a submarine delta deposit, against which inter- 

 pretation all its characteristics protest, we must consider that the lower 

 part of the series is of less areal extent than the upper, for this is true of 

 submarine as well as subaerial delta deposits, and so we come to the in- 



A. W. G. Wilson : Canadian Record of Science, vol. ix. No. 2. 100.°,. p. 120. 



