SNAKE MOUNTAIN. 263 



and the upper part calcareous, gradually passing into the pure Eolian limestones to the 

 eastward. Specimens of the mottled limestone or dolomite, called the Winooski lime- 

 stone, occur also at Snake Mountain. 



There is a peculiar reddish yellow color in the upper rock as it decomposes, that to a 

 practiced eye distinguishes it from everything else. The rock derives much of this color 

 from the peroxyd of iron. It may be seen by one riding along the road nearest the 

 mountain and examining carefully the appearance of the upper rock. This color distin- 

 guishes it particularly from the calciferous sandrock, with which it has been confounded. 



If we pass over the top of Snake Mountain and descend its eastern slope, we pass over 

 a cranberry meadow underlaid by liquid peat, and observe many interesting drift striae. 

 At Otter Creek the sandstone passes under the surface, and the next rock upon 

 the east is the eolian limestone /*, apparently overlying the former. The junction is not 

 seen, but the two rocks have been found almost in union three miles north in New 

 Haven. 



A similar section may be drawn, with the exception of the calciferous sandrock, at any 

 place in the range between Bridport (south part) and Charlotte ; and the junction of the 

 Hudson River group with the red sandrock may be seen much further, even to Canada. 



Prof. Emmons says that the fracture at the base of the mountain is "one of the most 

 interesting and remarkable of all the geological phenomena disclosed during the New 

 York survey." It can be followed from the north part of Bridport to Vergennes. 

 Beyond these limits we hesitate to prolong it. It seems gradually to die out at both 

 extremities, having its maximum in the section. Upon the figure the magnitude of the 

 elevation is indicated by the line m m, a dotted line showing the base of the present bed 

 before the action of erosion upon it. 



Prof. Emmons now supposes that in addition to the fault described there is another 

 fault at <Z, and that there is no rock present higher than the Trenton limestone; but that 

 the slates are all older than the Silurian, being the uppermost member of the taconic 

 system, namely, the black slate. We cannot discuss this subject here, but will simply 

 state one point relating to the discussion which is derived from this section. 



To suppose the black slate to be taconic makes it necessary to regard the cap rock of 

 the section, g, the same as the calciferous sandrock a, at the bottom of the mountain. 

 But they differ in two important respects. First lithologically, a is a limestone brownish 

 and decomposing black ; g is a variable rock, sometimes pure sandstone and then a mix- 

 ture of sandstone and dolomite. Besides it is generally red, and decomposes reddish 

 yellow. Its physical structure is different. Perhaps metamorphism would be adequate 

 to explain the difference of the lithological character. But, secondly, the lower bed con- 

 tains Maclurea matutina, while the upper bed contains no fossils whatever, except obscure 

 fucoids. There does not seem to have been a sufficient metamorphosis of the red sandrock 

 to obliterate so distinct a fossil as a Maclurea, if it ever existed. 



The evidence for the fault is not clear. If it was necessary to regard the red sandrock 

 as lower silurian, we should much prefer to regard it as the overlap of a great fold, pushed 

 so far that it covers a much higher rock. But this question is discussed elsewhere at 

 great length, in this Report. Nos. ^ to t -|g illustrate the Snake Mountain section in the 

 Cabinet. We proceed now to describe in detail the successive members of the lower 

 silurian system. 



