THE PERMIAN PERIOD 185 



that much of the disturbance must have occurred after the deposi- 

 tion of those strata. 



All through the vast time (at least 10,000,000 years) of the 

 Paleozoic era, a great land-mass (Appalachia) existed along what 

 is now the eastern coast of the United States. Its western boundary 

 was, most of the time, just east of the present Appalachians, while 

 it must have extended eastward at least as far as the border of the 

 continental shelf. Concerning the altitude and the character of 

 the topography of Appalachia we know almost nothing, but we 

 do know that it consisted of rock of pre-Cambrian age. The enor- 

 mous amount of sediment derived from it shows that Appalachia 

 was high enough during nearly all of its history to undergo vigorous 

 erosion. Although oscillations of level more than likely affected 

 the land-mass, and its western shore line was quite certainly 

 shifted at various times, nevertheless it persisted as a great land 

 area with approximately the same position during all of its long 

 history. Its general position is well shown on the various Paleozoic 

 paleogeographic maps. 



Barring certain minor oscillations of level, all of the region just 

 west of Appalachia was occupied by sea water during the whole Pal- 

 eozoic era, and sediments derived from the erosion of Appalachia 

 were laid down layer upon layer upon that sea bottom. The 

 coarsest and greatest thickness of sediments deposited nearest 

 the land, that is along what we might call the marginal'sea bottom. 

 At the same time, finer sediments and limestones in thinner sheets 

 were being deposited over much of the Mississippi Valley region. 

 By actual measurement, in the present Appalachians, we know 

 that the maximum thickness of these sediments was at least 

 25,000 feet. Now, since these are all of comparatively shallow 

 water origin, as proved by the coarseness of sediments, ripple- 

 marks, fossil Coral reefs, etc., we are forced to conclude that this 

 marginal sea bottom gradually sank during the process of sed- 

 imentation, thus producing what is called a great geosynclinal 

 trough. Perhaps the very weight of accumulating sediments 

 caused this sinking. Finally, toward the close of the Paleozoic era, 

 sinking of the marginal sea bottom and deposition of sediments 

 ceased, and a tremendous force of lateral compression was brought 

 to bear, causing the strata to become folded and more or less frac- 

 tured. Thus arose the great Appalachian Mountain range which, in 

 its prime, was doubtless much loftier than it is today (see Fig. 112). 



