14 NEW YORK STATE MUSEUM 



Taconic disturbance is most apparent in the eastern part of the 

 State where there exists a strong erosional unconformity between 

 the Lower and the Upper Siluric that is well marked also by basal 

 conglomerates (Oneida, Skunnemunk and Shawangunk) ; its appar- 

 ent influence can not be traced farther west than Oswego county, as 

 Vanuxem^ has noted that no break occurs in the succession from the 

 Lower Siluric to the Oswego sandstone of that section. 



The Upper Siluric formations, for the most part, have the char- 

 acters of shallow water accumulations. In the basal members sand- 

 stones and conglomerates prevail and are made up of the coarser 

 quartzose detritus from the wash of the nearby land. Some finer 

 sands and muds were brought down and deposited during Medina 

 time to form the shales which are interbedded with the sandstones, 

 but it was not until Clinton time that they came to be the predomi- 

 nant material. During this and the succeeding Rochester ages silts 

 were accumulated in great thickness, though there were brief periods 

 in the Clinton when they gave way to limestones and in eastern 

 New York to calcareous sandstones. With the beginning of Lock- 

 port time the conditions of sedimentation became favorable to the 

 deposition of limestones and these rocks were laid down all through 

 the rest of the Upper Siluric, with one notable interruption repre- 

 sented by the Salina shales. The changes in the character of the 

 sedimentation are to be regarded, doubtless, as reflecting a certain 

 amount of coastal oscillation which produced shallowing or deepen- 

 ing of the waters adapted to the different deposits. It is not neces- 

 sary to suppose, however, that the shales and limestones required 

 any great depths for their accumulation. On the other hand there 

 are unmistakable evidences that they were laid down for the most 

 part within the littoral reign. The Clinton and many of the over- 

 lying limestones are of fragmental character, composed of fossils 

 that were washed up on the old beaches where they were worked 

 over and ground by wave action. Abundant beach markings, such 

 as ripple marks, shrinkage cracks, worm borings and tracks of 

 crustaceans are to be found in the shales. 



During Clinton time there seems to have been an approach to the 

 conditions which later in the Salina age led to the extensive deposi- 

 tion of salt and gypsum. These conditions may have been initiated 

 even as early as Medina time. Salt springs are found not infre- 

 quently along the outcrop of the Medina sandstones and in such a 

 state of concentration that they were once used commercially for 



^ Geol. N. Y. 3d Dist. 1842. p. 61 et seq. 



