57 2 THE JOURNAL OF GEOLOGY. 



crumpling and slaty cleavage ; Dutton's a theory of mountain 

 formation. 



There has been no attempt to carry this idea of .Dutton's to 

 quantitative detail. It was probably thrown out as a suggestion 

 in mere despair of any other explanation, for he had already 

 repudiated the contractional theory. But the least reflection is 

 sufficient to convince that such slight want of complete isostatic 

 equilibrium as may sometimes occur would be utterly inadequate 

 to produce such effects. 



in. reyer's gliding theory. 1 



Prof. Reyer has recently put forward certain views fortified 

 by abundant experiments on plastic materials. His idea in brief 

 seems to be this : Strata are lifted and finally broken through by 

 up-rising fused or semi-fused matters and these appear above as 

 the granitic axis. As the axis rises, the strata are carried upward 

 on its shoulders, until when the slope is sufficiently steep the strata 

 slide downward crumpling themselves into complex folds and expos- 

 ing the granitic axis in width proportioned to the amount of 

 sliding. 



No doubt there is much value in these experiments of Reyer, 

 and possibly such gliding does indeed sometimes take place in 

 mountain strata and some foldings may be thus accounted for. 

 But the great objections to this view are ( I ) that there is no 

 adequate cause given for the granitic uplift, and (2) that it utterly 

 fails to account for the complex foldings of such mountains as 

 the Appalachian and Coast Range where there is no granite axis at 

 all. Reade, indeed, holds that the Piedmont region is the granite 

 axis of the Appalachian, and that the original strata of the east- 

 ern slope are now buried beneath the sea. But American geol- 

 ogists are unanimous in the belief that the shore line of the great 

 interior Palaeozoic sea was but a little east of the Appalachian 

 crest and the sea washed against land of Archaean rocks extend- 

 ing eastward from that line. 



1 Nature, Vol. 46, p. 224, 1892, and Vol. 47, p. 81, 1892. 



