THE CAYUGAN SERIES 537 



THE CATUGAN SERIES 



In southeastern New York the Shawangunk is overlain by the High 

 Falls red shales, and the usual interpretation is that both formations are 

 continuous in deposition. Even in the shafts in the Eondout Valley, 

 dug by the New York City Board of Water Supply, T. C. Brown 16 de- 

 scribes the contact as a gradual transition, and not an abrupt change 

 from the Shawangunk grit to the High Falls shale. However, in shaft 7 

 lie notes that the upper 6 to 8 feet of the Shawangunk consists of a coarse 

 conglomerate, and that this character is continued into the basal 2 feet 

 of the High Falls shale. To the writer these 8 to 10 feet are rather to 

 be interpreted as the basal beds of the invading High Falls shale, and the 

 great hiatus lies below these conglomerates. Nowhere in all of the many 

 places studied by the writer is there, however, convincing physical evi- 

 dence that there is a break between the equivalents of the Medina and 

 Salina deposits. This is clue to the condition that in most places the 

 contacts are obscured by weathering, and all that can now be said is that 

 the contacts must be of the disconformable type, because on one side of 

 the line the fossils of the green shales are of early Silurian time and on 

 the other side of Salina age. Even this conclusion is not easy to estab- 

 lish, and this can be clone only by tracing - the two series of deposits from 

 New York into Pennsylvania and Maryland. 



In the various sections described in Part II of this paper it is seen 

 that in the eastern ones the Shawangunk is always followed by a red 

 shale formation, and that in every case the actual contact between these 

 two series was not seen. However, just as soon as we strike westward 

 into the deposits farther away from the shore we meet with formations 

 intermediate in age between the Shawangunk and the Salinan series. 

 Forty miles across the basin from Shawangunk or Kittatinny Mountain 

 there occurs, in Jacks Mountain, above the Medina or Tuscarora, 1,043 

 feet of more or less greenish shales with occasional iron-ore beds, all of 

 which have marine organisms indicative of Clinton time. In other 

 words, as we go westward a great shale formation, intimately linked with 

 the Medina series, is wedged in between the Shawangunk and the Salina. 

 The writer has seen this stratigraphy in many places from New York to 

 Virginia, and if one disregards the fossils no striking break is anywhere 

 to be seen between the Clinton shales and the disconformably superposed 

 Salina shales. Again, in most places the actual contacts are obscured, 

 for they lie in the midst of two shale series. In Maryland, at Pinto, 

 however, the contact between them is well exposed, and only on the basis 

 of fossils, which can be had here immediately on either side of a deter- 



; Op. cit, pp. 471, 472. 



XXXIX — Boll. Gbol. Soc. Am., Vol. 27, 1915 



