118 



Rogers and his brother Professor D. H. Rogers* (one of our own 

 fellows), in working out the complicated folds and contortions of a 

 large region of palaeozoic rocks, is well known to every English 

 geologist who has visited North America. Placed at the head of 

 the State Surveys of Pennsylvania and Virginia, these gentlemen 

 took the occasion of the last meeting of the British Association to 

 send to this country a joint memoir, entitled, " On the Physical 

 Structui'e of the Appalachian Chain, as exemplifying the Laws 

 which regulated the elevation of great Mountain Chains ge- 

 nerally." 



The Appalachian chain, including the AUeghanies, is the great 

 back-bone of North America, having a length of nearly 1200 miles, 

 with average width of about 100 miles, and it is essentially composed 

 of one great mass of palseozoic deposits conformable to each other, 

 which these authors and others havie identified with Silurian f, De- 

 vonian and Carboniferous deposits. 



And here an acknowledgment is justly due to our able associate 

 and countryman, Mr. R. C. Taylor, well known to us before he left 

 this country for the United States, as the author not only of good 

 memoirs on the Crag of his native county, Norfolk, but also of an 

 accurate survey and model of a part of the Glaraoi-ganshire coal- 

 field. Mr. R. C. Taylor has, in fact, published several valuable sec- 

 tions and views explanatory of one of the coal-fields of Pennsylvania, 

 in a separate work on that country. 



Extending from north-east to south-west, the older rocks of the 

 Appalachian chain have been thrown into a number of anticlinal 

 ridges and synclinal valleys from 100 to 150 miles in length, and all 

 more or less parallel to each other, but with certain deviations from 

 rectilinear to curved dir/ections ; and of these Professors Rogers con- 

 stitute nine principal groups, in five of which the axes are straight. 

 Describing many of them, the authors show, that as the folds ap- 

 proach to the south-east, where igneous and crystalline rocks occur, 

 convolutions are much more rapid, accompanied by many breaks 

 and by complete inversion of the beds. This latter phEenomenon is 

 identified v^ith that which has been recognized on the flanks of the 

 Alps and other eruptive continental chains, where the older strata 

 are incumbent on younger, and on the western flank of our own 

 little Malvern Hills, where there is, as before said, a complete illus- 

 tration of inverted dip. Seeing also that, in proportion as they re- 

 cede from the main axis the folds are less abrupt, and gradually open 

 out into broad and flattened anticlinals, which entirely die away at a 

 certain distance from the crystalline and intrusive rocks, or towards 

 the interior, the authors formed a theory Avhich they conceive to be 

 applicable to the bending and elevation of strata generally. 



Comparing the undulations which mark the axes with the undu- 



* See his Report on American Geoiogy, published in the volumes of the 

 British Association. 



f The lowest rocks of the Appalachian chain were placed in parallel with 

 the Silurian rocks by Mr. G. W. Featherstonhaugh in 1836.^._ See, Geo], 

 Report. Washington, 1836, p. 101. . -..>;^'--.. 



