IIG JULES MARCOU ON THE TACONIC OF GEORGIA 



7. Red snndiock forming- the top of the hill. I did not make any ohscrvations on 

 that part of the section, nor farther east, Avhere are seen other shites and red sandrock 

 hills. 



1 have referred the red sandrock near the Missisqxioi river, No. 2, as belonging to the 

 Potsdam, and I see nothing in what has been jjublished by Mr. Walcott to change m}^ 

 view. As to the other expositions of red sandrock, marked Ko. 7, and farther east, I can- 

 not give any decided opinions ; they need to be carefully examined before any conclusion 

 can be reached. Perry says ''In some cases, the Black or S^vanton Slate (comprising 

 also the Phillipsbni'gh gronp) may be seen beneath the Potsdam sandstone (red sand- 

 rock), not only along its western flank, bnt also at the very edge of its eastern limits. 

 After long searching, I was at last so fortunate as to find the two i-ocks thus situated 

 and in immediate conjunction. This was on the easterly border of the sandstone, at 

 Shelburn Falls, Avhere, some years ago (in the summer of 1860) an excavation was made 

 in the channel of the La Plot river. Since that time, I have observed substantially the 

 same thing at man}' other points. So the Georgia Slate may be traced beneath the Pots- 

 dam sandstone (red sandrock) with ecpial clearness and shown to underlie it, in its ex- 

 treme extension eastward in Swanton."' 



There is no reasonable doubt that some portions of the red sandrock are younger than 

 the Georgia slates or formations and belong to the Potsdam sandstone. But the opinion 

 expressed by Mr. Walcott has also incontestably some basis, and the question must be 

 met by a new and very careful survey. 



My opinion is that two-thirds of Avhat is g'enerally called red sandrock belongs to the 

 Potsdam formation, and that one-third only is a part of the Georgia formation. I am 

 inclined to believe that those two different ages of red sandrock are in juxtaposition on 

 some part of the line of the outcrop of the Georgia formation. I think that a difference 

 in the dip of the two sei-ies is well marked l)y an angle of 10° or even 14°. On the west- 

 ern side of the red sandrock line, the dip is very small, the strata being almost horizontal, 

 or varying from 1° or 2-' to 6° or 8° at most; when, on the contrary, the red sandrock, 

 clearly belonging to lenticular masses inclosed in the Georgia slates, has an eastern dip 

 of 12° to 16°. 



IV. The supposed overlying great fault of the Georgia formation. — The 



SECTION at ChAELEBOURG NEAR QuEBEC. — LANDSLIDES AT MoNTMORENCT 



AND Indian Lorette Falls. 



I have previously said that Mr. Walcott regards the discordance of stratification on 

 the western limit of tlie r(!d sandrock as due to an overlapping fault of the Georgia for- 

 mation, which covers what he calls the Hudson river group, Trenton or Chazy, according 

 to localities. He thinks that the massive red sandrock was pushed over on the slates, 

 and consequently that the slates have been crushed, strongly compressed and forced mi- 

 der the red sandrock. 



The break and dislocations of the Taconic rocks are very great and the slates show 

 everywhere strong lateral pressure by their cleavage and their contorted and faulted 



'" Queries on tlie Red Sautlstone of Vermont, etc.," pp. 10 luul 11, Boston, I8GS (Ex. from rroc. Bust. lioc. Kat. Hist., xi.) 



