8o AMADEUS W. GRABAU 



E. THE MIDDLE SILURIC OR SALINAN 



This is typically known only from New York, Michigan, western 

 Ontario, northern Illinois, and Ohio, and is everywhere a series of 

 more or less calcareous shales and gypsiferous beds, with salt beds 

 up to ICO feet in thickness. The maximum development is in 

 central New York and southern Michigan, where it exceeds i,ooo 

 feet in thickness. In western New York it is only 350 feet thick. 

 The only fossils known from the beds are from the lower (Pitsford) 

 shales, where they represent the last survivors of the Guelph. They 

 are chiefly Eurypterids (Hughmilleria, Eurypterus, etc.) and occur 

 in muds alternating with dolomites carrying a Niagaran fauna. 

 The Eurypterid fauna also occurs in the mud layers in the Shaw^- 

 angunk conglomerate, which hardly admits of any other interpreta- 

 tion than deposition by torrential rivers. This would make the 

 Eurypterid fauna a fresh-water fauna, an interpretation which best 

 corresponds with the distribution of these fossils geologically as well 

 as geographically. The Salina series is best understood as a desert 

 deposit. The absence of organic remains (with the exceptions noted), 

 known to be abundant in all modern salt deposits of sea-margin 

 origin; the thickness of the salt beds; their limitation to circum- 

 scribed basins,' the red color of the lower shales, their mud cracks, 

 "Thongallen," etc., all point to a continental origin. The absence 

 of true marine strata of Salina age^ and erosion of the surrounding 

 Niagaran beds further indicate that North America was above water. 

 The salt was derived from the marine limestones of Niagaran and 

 , earlier age. 



THE GREEN POND SHAWANGUNK CONGLOMERATES AND SUCCEEDING RED SHALES 



The general retreat of the sea at the end of Niagaran time was 

 marked in the east by an uplift followed by continental sedimen- 

 tation. The series began with a conglomerate (Green Pond) 1,500 

 feet thick in northern New Jersey, but thinning northward to 500 

 feet at Ellen ville (Shawangunk conglomerate), to 200 feet at Rosen- 

 dale, and to nothing at Rondout. Southward and westward it thins 



1 See Walther, Gesetz der Wiistenbildung. Lack of space forbids the full discussion 

 of this interesting problem. It will be treated at length in another paper. 



2 The so-called marine Salina of Maryland is of Monroan age. 



