GEOLOGY. 245 



seen in the great mountain chains of America and Europe ? He sug- 

 gested, as the explanation of the phenomenon, the forward pressure of 

 the lava wave beneath, which he supposed to have produced the curve, 

 in the progress of an earthquake. If a horizontal stratum were acted 

 upon by a perpendicular force from within the earth, it would be raised 

 in a symmetrical arch ; but if this force had a horizontal as well as a 

 perpendicular action, the result would be the formation of a curve such 

 as is really found to exist. A railroad bar, breaking under the weight 

 of a passing train, is fractured towards the extremity farthest from that 

 on which the pressure commences ; and in the same way the points of 

 fracture in the curves of upheaved strata are at the most abrupt portion 

 of the curve, towards the termination of the wave. The point of frac- 

 ture in the railroad bar is nearer to its remote support in proportion 

 to the speed of the passing train. Prof. Rogers supposes that there is 

 a horizontal thrust acting upon the bar, through the principle of adhe- 

 sion, in addition to the perpendicular action of gravity. 



Mr. Desor stated, as an illustration of the rapid progress of geological 

 science, that the plication theory, which was hardly known fifteen 

 years ago, was now almost generally adopted ; and, with few excep- 

 tions, might be found even in the text-books. This great result, he 

 thought, was due chiefly to the investigations of Prof. Rogers, in the 

 AUeghany chain. As to the cause of the plication, several theories 

 had been proposed since that of Prof. Rogers. Prof. Studer, of Switr 

 zerland, thought that the plication of the Jura was the result of a lateral 

 pressure, caused by the upheaval of the Alps. Mr. C. Prevost ascribed 

 the plication to a bulging up caused by the depression of vast areas. 



Prof. Rogers said his own and his brother's views, in regard to the 

 upheaval of the mountain ranges, had been fully confirmed in his own 

 mind by visiting the Alps. He gave it as his opinion that the Jura 

 range was raised by a force from, the direction of the Vosges, as the plica- 

 tions all lean towards the Alps, not from them, as would be the case if 

 they had been caused by a lateral pressure, caused by the weight of the 

 latter, as supposed by Prevost. In many of the observed plications, the 

 upheaved strata preserve their shape by means of trap dykes, veins of 

 greenstone and quartz, which are always found in great numbers, occu- 

 pying the fissures on the abrupt surface of the curve ; and which, filling 

 these fissures in a liquid form, harden on cooling, and act as keys and 

 braces to prop up the bent strata. Proc. Boston Nat. Hist. Society. 



ON THE PASSAGE OF ANTICLINAL AXES INTO FAULTS. 



PROF. H. D. ROGERS, in presenting a communication to the American 

 Association, at Albany, under the above title, referred to the peculiar 

 structural features of the great south-eastern Appalachian belt, which 

 has its continuation in the district of New York, east of the Hudson, 

 and in Western Vermont. The series of folded axes or plications of 

 the strata in this prolonged zone, were first recognized and reduced to a 

 general law by Profs. II. D. and W. B. Rogers, more than ten years 

 ago, at the same time that the various phases or. gradations of anti- 

 clinal and synclinal axes were made the subject of examination. Prof. 



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