364 PROCEEDINGS OF THE ACADEMY OF 



by the cleavage planes. Between these plates of granite lie plates of un- 

 changed dark blue sandstone ; a rock which at the cascades (two miles from 

 the house in another direction) 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 practised topographical eye, the aspect of the whole White Mountain range 

 is that of synclinal erosion. 



Other considerations reinforce this opinion. The continuation and broaden- 

 ing of the range north-eastward through Maine and Lower Canada, where super- 

 3ilurian rocks abound, the termination of the range south-eastward before 

 reaching Massachusetts and Vermont, as the Alleghany synclinal stops at Catts- 

 kill 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 es- 

 carprrrent 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. 



Tl>e granite of Mount Osceola and the surrounding heights consists of large 

 crystals of feldspar, smaller crystals of quartz and smaller flakes of mica. 

 Here and there hornblende appears. The rock bears no resemblance to the 

 subfeilurian Highland and Blue Ridge range, and Adirondacks. It is friable 

 under the weather, shedding its crystals upon the ground under every over- 

 hanging ledge. The boulders are rounded by the weather action apparently 

 more than by movement ; for they have only travelled down the slopes be- 

 neath the cliffs from which they have fallen, and where those that remain are 

 sharp-angled. The peculiar gravel and sand of the Mad River Valley is a local 

 drift of similar origin. The metamorphism of these granites is considered by 

 Logan, Hunt, and others, as no longer disputable. They could easily originate 

 in the clayey sandstones of Formations VIII., IX. and X., of the Appalachians. 



Considering the whole White Mountain mass a synclinal plateau,then the sum- 

 mit of Mount Washington, which is such an acknowledged anomaly, becomes 

 regularly the single residual fragment of the highest formation which escaped 

 erosion. Its rock is so different in texture and structure from the rest of the 

 mountains that no other explanation seems possible ; and if this hypothesis be 

 adopted, there is no longer any need of that which supposes the submergence 

 of New England up to the base of the head of Mt. Washington and no higher, 

 leaving the head in the air to escape the general rounding and polishing 

 action. It becomes easy to consider the external difference due rather to the 

 difference of the rock formations above and below that horizon. 



It is to be hoped that a systematic explanation will be made of this interest- 

 ing region and the structure made out and mapped, so that we may arrive at 

 conclusions, instead of venturing conjectures. 



September 25th. 

 Vice President Bridges in the Chair. 



Thirty six members present. 



The Committee on the paper of Mr. John Cassin, " Descriptions of 

 New Birds from Western Africa in the Museum of the Academy of Na- 

 tural Sciences," reported in favor of its publication in the journal of 

 the Academy. 



On report of the respective Committees, the following papers were 

 ordered to be published in the Proceedings : 



[Sept. 



