S. W. Ford—Great Fault in Rensselaer County. 17 
ontories described in my former article. The rocks include 
-of limestone. Each of the promontories referred to contains a 
band of slates rich in graptolites, the best locality yet discovered 
occurring in promontory A, along the line of the Hudson River 
‘railroad, a few yards south of the flag-station at that point. 
Altogether this band has yielded fifteen species of graptolites, 
‘thirteen of which are well-known forms, and include G. serra- 
ulus, G. divarivatus and G. Whitfieldi. It has also furnished 
several specimens of a small Lingula, and an acephalous species 
probably identical with the Lyrodesma pulchella of Hall (Pal. 
Y., vol. i, p. 302, pl. $2, fig. 12). All of the beds have been 
greatly twisted and broken up, but their prevailing dip is east- 
ward at high angles. 
ines: | 
_ RENSSELAER COUNTY. \ COLUMBIA COUNTY. 
\ TOWN OF STUYVESANT. 
TOWNOF ScHODACK. \ Z—¢—— wea als 
1 @ ae 
LORRAINE SHALES. 
In its-extension southward into Columbia county, the visible 
area of the Lorraine becomes somewhat contracted, and bears 
a little to the westward; and directly in front of Mr. Patrick 
cCabe’s residence (M), it is completely cut off by a narrow 
marshy tract. Fifty yards south of Mr. McCabe’s, however, a 
low ledge of similar rocks is met with, having a width at the 
northern extremity of a few rods, and a run to the southward 
Of several hundred feet. The strike of the beds is a little east 
of north, the precise angle not determined. The slates of this 
ledge (c) have yielded the majority of the species of grapto- 
lites found in those of the promontories A and A’, and hence 
belong clearly to the same formation. At the date of publica- 
tion of my former paper they bad not been found fossiliferous. 
_ Upon the southeast, the rocks of the ledge just described are 
immediately succeeded by a widely different group of strata, 
the fossils of which prove that they belong to the Primordial 
‘Sroup in Jefferson county, and has the advantage, in its application to rocks of the 
‘Same age east of the Hudson river, of leaving the other formations which ther 
Occur uncompromised ; and for these reasons, and these alone, 1 have been led to 
Adopt it in my work. 
Am. Jour. Scr.—Tarmp Serres, Vol. XXIX, No. 169.—JAN., 1885. 
