EMMONS' AND LOGAN'S OPINIONS. 317 



views of the stratigraphical position of the shales west of the red sandrock, and the red 

 sandrock itself. Logan supposes (see his letter to Barrnade in another part of this Report) 

 that the red sandrock has been elevated independently of the Hudson River slates, and 

 was then folded over upon the latter, so that now an older rock rests upon a newer rock 

 conformally. Emmons supposes that if there has been any elevation, the slates have been 

 brought up with the red sandrock, and that the relations of the two to each other have 

 not been disturbed by any foldings or inversions of the strata. The red sandrock he sup- 

 poses to rest unconformably upon these slates. 



To illustrate these views, Prof. Emmons has given two figures in his American Geology, 

 Part //, pages 81, 82, representing the relative positions of the red sandrock and slates. 

 The locality of these sections is very near that of Figs. 228 and 229. He says: "At High- 

 gate, in Vermont, the Missisco passes through a gorge just below the bridge. The 

 calciferous sandstone [red sandstone] lines its banks on both sides, but some distance 

 below, the junction of the calciferous sandstone is entirely concealed, even at rather low 

 stages of water; and, from the irregularities of the slate which jut up, it appears that the 

 limestone might form a part of the group, by plunging down between the beds of slate. 

 On visiting this locality at a very low stage of water, I found that the calciferous rested 

 in an irregular trough in the slate and also upon its upturned edges. This fact explained 

 all the obscurities which had formerly raised doubts in my mind respecting the relations 

 of this rock to the slate ; and, besides, the folia of the slate are bent at the junction of the 

 two rocks, which in this case I attribute to the force which has been communicated to the 

 rocks, although it often occurs that folia of slate are puckered at the junction of a seam of 

 calc spar with the slate." 



In another part of this gorge, Prof. Emmons discovered an anticlinal in the slate, and 

 the grit rock is represented as lying unconformably upon the slates upon both sides of 

 the axis. We did not discover such a position of things in our hasty examination of the 

 spot, though we did discover an unconformability of the two rocks. There is certainly a 

 want of conformity between the slates and the grits, both at Highgate Falls and about 

 two miles further north, where Fig. 247 was drawn. 



The question to be decided now is, whether the want of conformity between these two 

 rocks in Highgate is found elsewhere, Avhether it is not a local affair. Even if it be ul- 

 timately decided that these two rocks are unconformable to each other, the decision will 

 amount to simply this : the grits overlie the slates unconformably. It does not decide 

 whether the slates are of the Hudson River age, or of the age of the Taconic slates, or of 

 the Georgia slates. There is no reason in the nature of things why the red sandrock 

 should not overlie the Hudson River Group unconformably. 



We think that a careful investigation of these rocks would show conclusively, from the 

 true or inverted position of rain marks, ripple marks, and shrinkage cracks, whether any 

 of them are inverted or not. We shall wait for such investigation before we give an 

 opinion on the subject. 



Further remarks upon this subject will be found in connection with the description of 

 Fig. 247. 



