Mat 31, 1907] 



SCIENCE 



867 



north progresses into steeper folding south- 

 westward, then into faulted folds and over- 

 thrusts, until in southern Tennessee and 

 northern Georgia faults are much more promi- 

 nent than folds. Huge overthrusts of many 

 miles throw extend from lower Virginia into 

 Georgia. These have been folded and faulted 

 by later deformation. In the mountains simi- 

 lar structures prevail and metamorphism is 

 added thereto. This increases rapidly toward 

 the southeast and in large areas has destroyed 

 the original aspect of the formations. 



These structures were produced by tre- 

 mendous force which thrust the pre-Oambrian 

 masses northwestward against the sediments. 

 According as these masses were unequally ad- 

 vanced the sediments were deformed and the 

 great bends of the Appalachian Valley pro- 

 duced. Most of the structures run for great 

 distances in parallel lines, but there are many 

 cross folds extending across the valley and 

 mountains. 



Deformation was active in pre-Cambrian 

 time, appeared in less degree at several times 

 during the Paleozoic, and culminated in the 

 post-Carboniferous Appalachian revolution. 

 The Piedmont Plateau shared to some extent 

 in the deformation of Triassie time, but the 

 rest of the region appears to have escaped. 

 Still later uplifts have appeared at various 

 times up to the Quaternary and can be traced 

 through the topographic forms. The land was 

 uplifted and warped in broad levels or domes. 



The Plateau Region: Mr. M. R. Campbell. 



The Appalachian Revolution: Mr. Bailey 



Willis. 



Assuming that the geologic structure of the 

 Appalachian zone is too well known to require 

 any descriptive statement, Mr. Willis pro- 

 ceeded to discuss the larger problems of the 

 nature and origin of the movement involved 

 in Appalachian folding. He referred to the 

 hypothesis which he had once entertained of a 

 movement of the interior continental region 

 from northwest to southeast, a movement sup- 

 posed to be of such a character that the mass 

 of ancient crystallines in North Carolina 

 formed the buttress against which Paleozoic 

 strata were folded. He gave reasons for 



abandoning this view and accepting that 

 which is more generally entertained, of a 

 movement from the southeast toward the north- 

 west. Tracing this northwestward movement, 

 he showed that all of the known mass of the 

 continent southeast of the Appalachian zone 

 had been involved in it ; that we must suppose 

 a belt a thousand miles long and several hun- 

 dred miles wide to have moved northwestward 

 between thirty and forty miles. With refer- 

 ence to such displacement of the continental 

 margin, he stated his belief that it involved 

 the expansion of a sub-oceanic sector. De- 

 veloping this idea by illustration of conti- 

 nental compression in North America and 

 Asia, he stated a general theory that since an 

 early geologic date, continents have from time 

 to time been compressed in consequence of the 

 expansion of the material beneath the oceanic 

 basins, and he attributed this expansion to the 

 plastic flow of rocks considered as rigid solids, 

 which are nevertheless not sufficiently firm to 

 maintain their form as masses of oceanic ex- 

 tent and one hundred miles or more deep. 

 This property of plastic movement would apply 

 equally to sub-continental as to sub-oceanic 

 masses, but in view of the greater density of 

 the latter, the motion has been from the 

 oceanic toward the continental areas. 



Economic Conquest of the Southern Appa- 

 lachian Goal Field: Mr. Geo. H. Ashley. 

 Mr. Ashley traced briefly the movements 

 resulting in the populating of the district, 

 pointing out some of the factors affecting that 

 movement, the routes by which it took place 

 and the relation of those routes to the physi- 

 ography. He then reviewed briefly the early 

 efforts in marketing the coal by the use of the 

 rivers reaching from the Ohio up into the 

 coal fields, pointing out the difficulties en- 

 countered and how these were overcome by 

 building dams and locks. Then came a study 

 of the gradual incoming of railroads in which 

 he pointed out the relation of the routes 

 chosen to the physiography, some of the dif- 

 ficulties encountered, and the territory opened 

 up to export as a result. 



Ealph Arnold, 



Secretary 



