S. W. Ford—Great Fault in Rensselaer County. 19 
ant, in front of which, and all the way to the bottom of the 
ravine which it faces, the Lorraine beds are concealed by drift. 
The opposite slope is to some extent similarly mantled over; 
but the character of the underlying beds has been well ascer- 
tained. 
N.W. 3 S.E 
rN 
‘a em aN 
> Sig ty, 4 Y 
8 feg'e 
? 1S, AS < 
e , “as LOWER POTSDAM GROUP. 
In the second section (fig. 2), the two groups are shown in 
contact with each other, and the fault is located with precision. 
Beyond this the section does not appear to me to call for special 
comment. On tracing the Primordial rocks eastward over the 
country, they are found to be arranged in a series of rather 
broad synclinal folds with apparently intervening denuded 
anticlinals. I have not yet attempted to trace out the course 
of the fault in its more eastward extension. 
4 have purposely dwelt at some length upon the structure of 
this remarkable region, partly because of the great interest 
which it possesses, and partly because of the efforts that have 
been put forth during the past two or three years, to banish 
from geology altogether what has, I believe, with good reaso 
been denominated “The Great Appalachian Fault.” These 
efforts have been grounded mainly upon the results of inyesti- 
gations conducted upon the west side of the Hudson river, and 
‘aving no real bearing upon the question. One writer, in par- 
ticular, whose views have appeared during the period referred 
to,* has pronounced the Great Appalachian Fault to be purely 
-hypothetical, principally upon the strength of field-work done 
in the vicinity of Rondout; and a disposition seems to have 
Sprung up in other minds, at about the same period, to advo- 
cate a similar view. To those who may have been led, either 
y their own investigations, or the researches of others, to so 
regard the matter, the region herein described is respectfully 
recommended, as one well calculated to conduct to the opposite 
conclusion. 
Schodack Landing, N. Y., Oct. 20th, 1884. 
' 
go” Mee, M, Davis, on “The Non-conformity at Rondout, N. Y.” This 
Journal for November, 1883. 
