22 PROCEEDINGS OF MADISON MEETING. 



by a broad, submerged plain surrounding them and their neighbors and merging 

 with the submarine plain flanking the Atlantic and Gulf coasts of th^ mainland ; 

 and the plain circumscribing the islands is nearly as broad and continuous as that 

 skirting the continent. Thus the submarine configuration would seem to connect 

 and bind into unity the island-continent and the mainland. Now the age of the 

 portion of this plain skirting the mainland is known, and it is significant that the 

 plain does not represent a single episode or period, but has been in continuous 

 process of accumulation since the beginning of the Cretaceous, if not the end of 

 the Triassic ; and it may accordingly be questioned whether the submarine shelf 

 circumscribing the islands does not indicate equal antiquity, the somewhat greater 

 width of the shelf along the American shore being counterbalanced by the greater 

 width of tributary land area. This would carry the profound movement of the 

 Bahaman region back to a period of profound movement in the mainland, indeed 

 to the birthdate of our southeastern province and the drowning of the older land 

 whence the Appalachian sediments came. 



Warren Upham : 



Concerning the time of erosion of the submarine valleys on our Atlantic coastal 

 slope, it is especially noteworthy that they are cut in a descending plain of Tertiary 

 and underlying Cretaceous beds ; and the same condition is also known, by Mr J. 

 Y. Buchanan's description, for the Congo valley or canyon cut in the submerged 

 Tertiary border slope of the African continental plateau. In both regions the high 

 epeirogenic uplift and accompanying stream erosion were evidently of late Tertiary 

 and Quaternary age. If any long time had passed since the subsidence of the 

 African continent, the muddy Congo waters must have filled both the very deep 

 lower part of that river and the continuation of its valley oflshore. Such great 

 crustal oscillations in high latitudes, lifting the lands now overspread by the glacial 

 drift, seem to me to have been probably the chief cause of the accumulation of 

 their ice-sheets. 



C. D. Walcott: 



The sediments deposited in the Appalachian sea during earlier Paleozoic time 

 were largely derived from an elevated land area to the eastward, and it is probable 

 that this area furnished sediments throughout Paleozoic time and was several times 

 eroded to base-level and in turn elevated to supply additional mechanical sedi- 

 ments to the Appalachian sea. The extent of this elevation is unknown, but it 

 must have been considerable. When the final depression of the Atlantic coast 

 area took place, it appears to have been largely on the line of the fault forming the 

 '' fall-line" between the Coastal plain and the Piedmont plateau region. 



While it is evident that there has been a most extensive elevation of the south- 

 eastern portion of the continent, there is no proof that the continent as a whole 

 has ever been correspondingly depressed beneath the ocean's water. Nowhere on 

 the surface of the continent have deposits characteristic of the deep sea been dis- 

 covered. On the contrary, all of the sedimentary rocks were deposited in interior 

 or marginal seas within the limits of the continental plateau ; also it is not in evi- 

 dence that the relative position of the deep sea and the continental plateau has 

 changed since Algonkian time. 



Mr Spencer's contribution to the subject of the epeirogenic movements of the 

 continent is a most interesting and valuable one, and I shall look forward with 

 great interest to the publication of his memoir. 



