THE SILURIAN SECTIONS 543 



series and as indicative of a break between the Lower and Upper 

 Silurian. 



Probable break here. 



Silurian. 



Shawangunk conglomerate. Thickness variable between 170 and 280 feet. 

 In general the formation is a pure white quartz sandstone with zones 

 of conglomerate that are most prevalent toward the bottom and top. 

 There are also occasional thin zones (up to 1 foot) of green shale and 

 black shale (less than 1 inch thick). 



Ordovician. 



Marked unconformity. All of Richmondian absent. 

 Hudson River shales. 



Green Pond Mountain, New Jersey. — East of all the other localities. 

 Based on the work of Darton: Bulletin of the Geological Society of 

 America, volume 5, 1894, pages 382-385; Kiimmel and Weller: Annual 

 Eeport of the Geological Survey of New Jersey for 1901, 1902, pages 

 9-15 ; Graban : Bulletin of the Geological Society of America, volume 24, 

 1913, pages 477-479; and Barrell: American Journal of Science, volume 

 37, 1914, pages 234-239. This area is about 23 miles to the east of 

 Shawangunk Mountain and is the most easterly Silurian area of the 

 Appalachian trough. The strata lie in a much folded and faulted syn- 

 cline, so that it is difficult to get their exact thicknesses. 



Silurian. Cayugan series. 



Longwood shales. Below the Helderbergian (Decker Ferry) there occurs 

 in Longwood Valley, east of "Middleton," a soft, sandy shale series, 

 much cleaved, mostly of a bright red color, with interbedded lighter 

 colored zones. The thickness is estimated at 200 feet. 



Probable break. Darton describes the Longwood shales as grading into 

 the Green Pond conglomerate, but if the former is Salina in age, as 

 the present writer correlates it, and the latter is the equivalent of the 

 Shawangunk, then there is a marked stratigraphic hiatus between the 

 two, with all of the Niagaran series absent. Kiimmel and Weller state 

 that the Green Pond passes upward somewhat abruptly into the soft 

 red Longwood shale. 



Green Pond conglomerate. Consists in the main of coarse red and greenish 

 conglomerates below and buff and reddish quartzites above. The sub- 

 angular and well-rounded pebbles vary in size up to 3 inches and are 

 embedded in a hard, sandy, quartzitic matrix of dull red color. The 

 pebbles are "almost entirely white quartz, but some pink quartz, black, 

 white, yellow, and reel chert, red and purple quartzite, and a very few 

 red shale and pink jasper pebbles occur." "The thickness of this for- 

 mation is probably not less than 1,200 feet, and locally it may be 1,500 

 feet" (Kiimmel and Weller). 



Ordovician. 



