278 ANNUAL OF SCIENTIFIC D.'SCUVEUY. 



printed on the same sheet with it, having a scale of 1 : 000,000, one of which 

 gives the White Mountains of New Hampshire, the other the Black Moun- 

 tains of North Carolina, both according to Mr. Guyot's measurements. 

 Silliman's Journal, Nov. 1800. 



ON THE GEOLOGY OF THE WHITE MOUNTAINS. 



At a recent meeting of the Philadelphia Academy, Mr. J. P. Lesley com- 

 municated the result of some recent observations on the Geology of the 

 White Mountains of New England. His examinations of these mountains 

 had led to the conviction that the range would prove to be synclinal instead 

 of anticlinal, and therefore probably of Devonian age. A section which he 

 made in 1857 along the Grand Trunk Railroad showed him the synclinal 

 structure, with comparatively few dips, and at least two main anticlinal 

 divisions. The profile in the Franconia notch is evidently a cliff outcrop of 

 a horizontal plate. The newly opened Greely Mountain House in Water- 

 ville, in a cul-de-sac valley at the head of Mad River, and six or eight miles 

 in an east line through the woods from the Flume House, is surrounded by 

 bold outcrops of nearly horizontal massive plates of granite. Ascending 

 Mad River from Campton, the traveller has the White-face range on his 

 right, with apparent gentle dips to the northwest. But on his left he has 

 the Welsh mountain range and Mount Osceola, with an unmistakable and 

 universal dip, never over fifteen degrees, and much of it under ten degrees, 

 to the southeast, which can be studied for at least seven miles, northeast 

 and southeast. Turning to the left and ascending Mount Osceola (which 

 Mr. Lesley found by barometer to be over 2000 above the Greely House, and 

 therefore not much lower than Mount Lafayette), the bridle path mounts 

 over successive outcrop edges of perfectly horizontal plates of granite, as 

 evidently and regularly bedded as any of the sandstone masses of the Alle- 

 ghanies, the bed planes not being at all disguised by the cleavage planes. 

 Between these plates of granite lie plates of unchanged dark blue sandstone, 

 a rock which at the cascades (two miles from the house in another direc- 

 tion) has been mistaken for greenstone trap. The successive terraces and 

 cliffs of the mountain are evidently the consequences of this horizontal 

 and alternate structure. As in other horizontal mountain plateaus, the 

 terraces here are projected between the ravines in the form of noses, with 

 straight crests, and terraced or stepped at their ends. In fact, to a prac- 

 tised topographical eye, the aspect of the whole White Mountain range is 

 that of synclinal erosion. 



Other considerations reinforce this opinion. The continuation and broad- 

 ening of the range northeastward through Maine and Lower Canada, where 

 super-silurian rocks abound, the termination of the range southeastward 

 before reaching Massachusetts and Vermont, as the Alleghany synclinal 

 stops at Catskill before crossing the Hudson, the presence of horizontal 

 rocks at Worcester, and, more generally than would be supposed, through 

 middle New England, the fact that the Connecticut valley runs everywhere 

 under the western escarpment of the White Mountains, separating it from 

 the Silurian range of the Green Mountains, and the presence of Potsdam 

 and other low formations in eastern Massachusetts, all these facts would 

 find their explanation in a synclinal terminal eroded structure of the White 

 Mountain mass. 



The granite of Mount Osceola and the surrounding heights consists of 



