Shaler.] 



118 [February 1, 



the foot of the Alleghany chain all the way from North Carolina to 

 Vermont. Throughout this line it is more or less disturbed by dislo- 

 cations, the directions of which coincide quite closely with that of the 

 Richmond ridge and the faults of the "coal-field just west of it. In 

 Massachusetts these dislocations are distinctly seen in the great faults 

 of the Connecticut valley which hare given us the ridges of the 

 Mounts Tom and Holyoke range, the Greenfield trap ridge, and 

 many other similar reliefs. 



If we could assume that these dislocations, which have cut up the 

 Connecticut equivalents of the Richmond beds, were produced at the 

 same time as the uplift of the Richmond axes, or the faults of its coal 

 basin, we should be near the determination of the age of these dis- 

 turbances. 



The Connecticut river system of dislocation seems to be continued 

 in parallel disturbances to the eastward, as far as Martha's Vineyard, 

 the principal faults and folds of which have a north, south, and south- 

 west trend. On this island the disturbances have upheaved beds of 

 the Miocene age, so that we are led to suspect, on good grounds, that 

 the whole system of north-west and south-west breaks, so extremely 

 developed between this point and the foot of the Berkshire hills, are 

 of this recent age. The recent look of the Connecticut valley dislo- 

 cations, upon which the erosion which has always been active in this 

 region has acted to a very slight extent, seems to corroborate this 

 view; but it would be hazardous to say that the Virginia dislocations, 

 which cut rocks of the same formation, and have near the same 

 course, are to be regarded as of the same age. All that these corres- 

 pondences can be regarded as establishing, is the probability of such 

 a relation of age, a probability which must be carefully weighed with 

 the other evidence before we can give it much weight. These Vir- 

 ginia dislocations have undoubtedly been much more eroded than 

 those of Massachusetts, inasmuch as despite the powerful disturbance 

 produced by the elevation of the Richmond axis, and the great faults 

 of the coal basin, the region in which they occur is nearly level. 

 There is reason to believe that the sea has worked more constantly 

 against the reliefs produced by these dislocations than upon those of 

 Massachusetts, which have probably never been subjected to the pow- 

 erful erosion of the oceanic waves . Unless we can attribute the dis- 

 appearance of all these irregularities of surface to some such differ- 

 ence of conditions, we must certainly assign to them a much earlier 

 period of uplift. Taking the facts altogether, it seems reasonable to 



