No. 2.] THE PRIMORDIAL ROCKS OF TROY. 209 



NOTES ON THE PRIMORDIAL ROCKS IN THE 

 VICINITY OF TROY, N. Y. 



By S. W. Ford. 



(^From the American Journal of Science and Arts, Vol. II., July, 1871.) 



In view of the prevailing uncertainty respecting- the age of the 

 rocks of that portion of the Taconic series of Profes-sor Emmons 

 lying east of the Hudson river, I was led several years ago to 

 undertake the investigation of some of these rocks in my own 

 neighbourhood, though I had but few hopes of learning anything 

 essentially new about them. It soon became apparent that much 

 valuable information might be obtained from them ; and from 

 certain facts which early came under my observation I was induced 

 to continue their study. I propose here to notice briefly some of 

 the more noteworthy results thus far obtained. 



The rocks immediately east of the Hudson at Troy are fine, 



black, glazed shales, with occasional sandy layers, and have usually 



been regarded as belonging to the Hudson River formation. They 



have been greatly crushed, but their general dip is evidently 



eastward, and at a high angle. They extend eastward about 



half a mile, and form a hill of considerable maanitude within the 



city limits. Following the course of this hill northward, we find 

 them frequently well exposed in railway cuttings, and before 



reaching Lansingburgh, which is three miles distant, in a bold 



elevation several hundred feet in heiiiht. 



The only fossils which these shales have afforded, are the ob- 

 scure form described under the name of DiscojyJii/Uum peltutum 

 (Pal. N. Y., vol. i, 277, plate Ixxv, fig. 3), and two or three species 

 of graptolites, the latter having been but recently obtained. The 

 graptolites resemble closely certain well-known Hudson river forms, 

 but whether certainly identical I am at present unable to state. 

 If truly Hudson river shales, then the absence of any other fos- 

 sils in these rocks, except those above mentioned, appears not a 

 little remarkable. 



Upon the east, after an interval of concealment varying some- 

 what in different localities, these shales are followed by the 

 widely different rocks of the " Taconic " series, likewise dipping 

 Vol. VI. P No. 2. 



