1912. 



NATURAL SCIENCES OF PHILADELPHIA. 



447 



Large Southern Reef; (2) The Channel, and (3) The Small Northern 

 Reef. 



The Large Southern Reef. — As we follow the shore of the lake 

 northwestward from Spafford Landing (Skaneateles Quadrangle, 

 U. S. G. S.), the corals first appear above water level on the north 

 side of a small point known locally under the terms Ivy Point and 

 also Willow Point. The reef at its first appearance ranges from 

 3.5 feet to 4 feet thick and is made up almost entirely of the hard 

 parts of Zaphrentis, Heliophyllum, and Cystiphyllum, together with 

 the silt which filled the interstices between the growing corals and 

 brought an end to their growth. The reef maintains this uniform 

 character and thickness as far northwestward as the point known 

 locally as Staghorn Point — a distance of approximately two-thirds 

 of a mile. From Ivy Point the reef rises gradually for a ways, then 

 runs with little or no dip well up toward Staghorn Point, where the 



N W 



Otaiylwn It 



Diagrammatic northwest-southeast section of the Staghorn Point Coral 

 Masses in the Hamilton Shale of Skaneateles Lake, N. Y. 



Reefs in solid black. Shales in lines. Channel and reef-margin deposits in 

 lines and dots. S = Southern Reef. C = Channel. N = Northern Reef. 



dip increases. Its base is from 1 to 2 feet above high-water 

 mark just south of Staghorn Point. Throughout this distance 

 (from Ivy Point to Staghorn Point) the reef is apparently entirely 

 conformable with the beds above and below. It is underlaid by 

 thickly bedded hard limy shale, which carries a characteristic Hamil- 

 ton fauna rich in brachiopods and mollusks. It is immediately 

 overlaid by shales carrying a sparse fauna, the typical Hamilton 

 assemblage reappearing a few feet above the reef. In the reef 

 itself the species of brachiopods and mollusks, so abundant through- 

 out the rest of the Hamilton, are almost entirely lacking. 



Just north of Staghorn Point the base of the reef is about 5 feet 

 above the lake level and its thickness has fallen to about 3 feet. 

 For a distance of about 700" feet northward the reef rises until it is 



