. 
16. S. W. Ford—Great Fault in Rensselaer County. 
V.—- Observations upon the Great Fault in the vicinity of 
2 aihudeck Landing, Rensselaer County, N. Y.; by S. W. Forp. 
IN an earlier paper by the writer, upon the age of the rocks 
in the vicinity of Schodack Landing (this Journal for Sep- 
tember, 1884), the exact course of the great fault referred to, or, 
in other words, the precise age of a ledge of slaty rocks a short 
of th 
distance south e more southerly “promontory therein de- 
obtain fossils from the rocks in dispute, and, as will be seen 
further on, by the extraordinary position of the adjacent beds. 
I have recently spent oe days in a careful study of the ye 
locality, and in further examinations of the rocks of 
neighborhood ; and the additional facts obtained form the site 
ject-matter of the present article. 
It is not often that one is permitted to observe the slates or 
schists of the early Cambrian overlying in apparent conformity" 
those at the summit of the Lower Silurian, and yet such is the 
case in the locality which I am about to describe.* Along the 
Adil bases of Snake and Buck mountains in Vermont, and 
also in the hills east of Troy and Lansingburgh, New York, 
contact of the older and newer groups been observed. In order 
to render the subject clearer to those who may be unacquainted 
The dotted area of the m map represents that portion of the 
district occupied by the Lorraine Shales (= Hudson River 
Group),t and the particular portions of it, A, A’, the two prom- 
* Judging from the life-history of the Trilobite Olenellus asaphoides, as pr 
present known, I should infer that the Troy and Stuyvesant Primordial beds 
Tam aware, any evidence that would warrant their separation from them as 4 
distinct group, or their assignment to an independent —. horizon. 
ave edge the designation “Hudson River Group,” for the reasons (1) 
that the rocks of this group constitute, in all probability, but a small proportion 
of the terranes eas be of the Hudson river to which the name was originally and 
especially EE (2) that the term, as a geographical one, has come to be mis- 
ae as will be seen by the map of the Schodack bs ed and (3) that 1t has 
term Taconic, The old synonym, “ Lorraine,” see for 
