86 FROM FISH TO PHILOSOPHER 



At the close of the Devonian the earth suffered its 

 third major upheaval in vertebrate history— the Acadian 

 disturbance, named from Acadia of Maritime Canada 

 where the Devonian and imderlying sediments remain 

 exposed today as greatly uplifted and tortuously 

 wrinkled strata. The Acadian disturbance culminated in 

 a second generation of Appalachian Mountains running 

 along the line of the older (Ordovician) Taconic range; 

 it is estimated that in this one area alone the Acadian 

 uplift exceeded the volxmie of the present Sierra Nevada, 

 a range 75 to 100 miles wide and 400 miles in length, 

 and rising to nearly three miles above sea level at its 

 crest. Volcanic activity was marked in southern Quebec, 

 the Gaspe Peninsula, New Brunswick, and Maine, 

 wherever the crust was broken by deep faults, while con- 

 tinued uplift and erosion exposed the basal continental 

 granite in Maine at Moimt Katahdin, and in the White 

 Mountains— the latter once rising at least 12,000 and pos- 

 sibly 17,000 feet in height. Early in the interval follow- 

 ing the Acadian uplift an inland sea spread over what 

 is now the Mississippi Valley and there laid down the 

 rich fossil record which gives to the early American 

 Carboniferous its name. 



The Ouachita disturbance, which closed the Missis- 

 sippian, is considered by some historical geologists to be 

 the forerunner of, and essentially integral with, the great 

 Appalachian revolution that was ultimately to close the 

 Paleozoic era and bring about profound transformations 

 in all forms of life. Between Mississippian and Pennsyl- 

 vanian time the eastern and southern parts of North 

 America had again been greatly elevated, and mountains 

 had begun to rise in Colorado and South Dakota, to form 

 the Colorado Mountains (the Rockies are of more recent 

 origin); so that near Leadville, Colorado, for example, 

 marine limestone which was laid down in the Mississip- 

 pian now lies two miles above sea level. But even as the 

 eastern and western edges of the continent rose and 

 buckled into mountain chains, the central basin sank ir- 



