GEOLOGIC HISTORY. 393 



Geologic History. 



The trough in which the formations in the Green Pond-Shunnemunk 

 belt lie, appears to be due to a narrow area of Cambrian limestone either 

 deposited in a narrow inlet or, more probably, faulted down among the 

 crystalline rocks. The erosion of this limestone wedge in early Paleozoic 

 times afforded a long, narrow basin in which more or less shale was de- 

 posited in Hudson times. As this was followed by a period of uplift 

 and erosion, in which more or less of the shales were removed, the posi- 

 tion of the old shore line of Hudson deposition cannot everywhere be 

 determined, and its southern termination is altogether in doubt. It 

 probably extended at least as far south as Newfoundland. About New- 

 foundland and to the southward the crystalline rocks were bared at the 

 beginning of deposition of the Green Pond beds, and were submerged by 

 the general subsidence which inaugurated Upper Silurian deposition in 

 eastern New York. As the conglomerates and quartzites are exhibited 

 mainly along the eastern side of the basin and to the southward, it is 

 suggested that the submergence was such that deposition was restricted 

 to this area, for their relations to immediately succeeding formations indi- 

 cate that they have not been widely removed by erosion. This period 

 was continued by the deposition of the red shales of the Longwood series, 

 the Helderberg limestones, and the Oriskany sandstones in continuous 

 succession. The shales and limestone indicate increasing submergence 

 and overlap, which appeared to have continued in the Oriskany depo- 

 sition in part of the area. This condition in Oriskany times is indicated 

 by the apparent almost general overlap of the Oriskany beyond the edges 

 of the Helderberg beds west and southwest of Skunnemunk mountain, 

 but that it is not general is shown by the absence of Oriskany deposits 

 between the Helderberg limestone and Monroe shales in Pine hill north 

 of Monroe, and at the locality on the Avest side of Bellvale mountain. 

 The coarseness of the deposit indicates an abrupt change of conditions, 

 which abruptly terminated the deposition of the Helderberg limestones. 

 As a change of this character usually immediately follows uplift the rela- 

 tions here are somewhat anomalous. They may be due to increased 

 submergence having given access to stronger currents which brought 

 in the coarse materials. This, however, is merely a suggestion. 



The Monroe shale deposition was attendant on increased submergence 

 and the deposits overlapped the preceding formations and the crystalline 

 rocks in part. Probably they were laid down over a wide area, for they 

 have since been widely removed by erosion. 



The Skunnemunk conglomerate probably overlapped the crystalline 



