Prosser and Cumings — r LowER Silurian Sections. 



of the massive, light grey Calciferous sandrock and is one <»i the best out- 

 crops of the formation to be found in the Mohawk valley. A specimen of 

 Oryptozoon proliferum, Hall, was found near the middle of the cliff. 



B A . In the field south of the cliff, mostly covered, showing only 

 occasional outcrops of the Calciferous sandrock with a conspicuous stratum 

 at the top of the first terrace south of the cliff. 



£ 5 . Partly covered, still showing plenty of outcrops of an arena- 40^490 

 ceous, compact, greyish rock with irregular fucoidal markings. Several 

 specimens of Ophileta complanata, Van., and also the form named O. levata 

 by Vanuxem*, have been found in the somewhat shaly layers of this division. 

 The Calciferous sandrock caps the highest land about one mile southwest of 

 the railroad cliff, although it is undoubtedly near the summit of the 

 formation. 



The above section shows that the Calciferous formation has a thickness 

 of 500 feet in the region of Sprakers and the lower gorge of the Mohawk 

 river. This decided increase over the supposed thickness will be appreciated 

 when it is stated that Vanuxem gave it as " upwards of 200 feet thick at the 

 Noses and Little Falls."f Darton states that " the formation has a thickness 

 of 200 to 250 feet on the Mohawk, and the amount appears to be constant 

 over a wide area."J The thickness of the Calciferous sandrock along the 

 Mohawk valley is thus shown to be 500 feet which is some 250 to 300 feet 

 greater than has generally been given. 



Section at Yosts. 



On the northern side of the Mohawk river at Yosts, three miles below 

 Sprakers and five miles above Fonda, is a high and steep cliff composed of 

 the Calciferous sandrock. This locality is at the eastern end of the lower 

 gorge of the Mohawk river and the massive, nearly horizontal layers of the 

 Calciferous formation are conspicuously visible from the trains of the New 

 York Central railroad. (See Plate I.) 



VI C 1 . Covered from the railroad track to the base of the cliff. u i~\isi 

 The greater part if not all of this covered division belongs in the Calciferous. 



C'~. Massive layers of Calciferous sandrock, forming the nearly aw^MB 

 perpendicular cliff. From the base of the Calciferous ledges to the brow of 

 the cliff. 



* This species is referred to O. complanata by Whitfield. See Bulletin American Museum of Natural History, Vol. II : p. 40 

 t Geology of New York, Part III, p. 32. On p. 205 Vanuxem stated that the Calciferous cliff at the Noses " rises vertically to 

 two huudied aDd more feet." 



J Tliirieenth Annual Report of the State Geologist [New York], p. 418. 



