904 PRINCIPLES OF STRATIGRAPHY 



the Appalachians commenced, the strata were practically horizon- 

 tal and the upper surface of the youngest beds essentially at sea- 

 level, and assuming, furthermore, that the higher Carbonic and 

 Permic beds of the region (above the Potts ville) was i,ioo 

 feet thick, Chamberlin concludes that 3 miles represents the average 

 height of the top of the restored Pottsville conglomerate over the 

 area from Tyrone to Harrisburg, i. e., the vertical deformation was 

 of that amount. 



There are here several assumptions which need careful consid- 

 eration before we can regard this as anything more tiian a very 

 general estimate. In the first place, if we regard the late Paheozoic 

 sediments as terrestrial in type rather than marine, as their nature 

 seems to indicate, we can not assume an initial horizontality with 

 the upper strata at sea-level throughout. Even on the basis of the 

 gentle gradient of the present delta-fan of the Huang-ho the eleva- 

 tion at the heads of the delta plains would be some 500 feet or 

 more above sea-level, and from the coarseness of the material in 

 the deposits it is likely that this elevation was a thousand feet, if 

 not more. 



In the second place, it appears that the estimate of the original 

 thickness of the post-Pottsville Palaeozoic is much too low. A 

 comparison of the thickness of the Pottsville and Kanawha forma- 

 tions between the eastern and western portions of their outcrops 

 shows the thickness of these two formations in the western region 

 to be only one-fifth or one-sixth that of the part preserved in the 

 eastern Appalachians. Since the sediment of the later formations 

 was also derived from the Appalachian old land, and since the 

 nature of the deposit suggests a similar origin of the later strata, 

 it does not seem amiss to consider that a similar eastward increase 

 in thickness originally obtained in the case of these higher strata as 

 well. This would make the Allegheny alone some 1,500 or more 

 feet in thickness in the Appalachian region, while the remaining 

 formations, if increased at the same rate, would aggregate 11,000 

 or 12.000 feet, making a total above the Pottsville in round num- 

 bers of about 13,000 feet of strata. This is not an improbable 

 thickness when we consider the 15,000 feet of late Tertiary delta 

 deposits of the Siwalik formation of India (see ante. Chapter 

 XIV). 



Character and Thickness of the Deformed Mass. On the 

 assumed elevation of about 3 miles for the entire area, Chamberlin 

 figures out the thickness of the part of the crust involved in the 

 folding. Since different sections have been differently affected, 

 he considers each independently with the following results : 



