180 WALKS AND TALKS. 



of any system. There is always a great limestone formation 

 from the middle to the upper part of the system not always 

 extending to the top of it and this is generally quite con- 

 spicuous, in consequence of its solidity and prominence and 

 great usefulness. The great central limestone mass of a system 

 may be traced through all the windings of its outcrop, by a 

 line of quarries and cliffs and rocky ridges. If you can say 

 where this conspicuous central limestone belt is located, you 

 can at once understand that the older strata of the system 

 must lie on the side from which the limestone dips, and the 

 newer strata must lie on the side toward which the limestone 

 dips. Now, the great limestone mass of the Devonian is the 

 Corniferous Limestone. Throughout the west, the overlying 

 Hamilton formation is also a limestone, though mostly shaly 

 at the east. The limestone mass, therefore, from Ohio west- 

 ward, is Corniferous-Harnilton. Some of the points where 

 the Devonian limestone mass rises conspicuously are the fol- 

 lowing : Syracuse, Leroy, Caledonia, Buffalo, Ingersoll, Lon- 

 don, Sandusky, Kelly's Island, Columbus, Monroe, Alpena, 

 Mackinac, Petoskey, Rock Island, Iowa City, Louisville. At 

 all these points we find a limestone of nearly the same age, 

 containing generally an abundance of marine fossils. The 

 corals are very conspicuous, and at the Falls of the Ohio, and 

 the head of Little Traverse Bay, appear to have been gathered 

 together in literal reefs. The former locality and its vicinity 

 has been a favorite collecting ground for many years, and 

 geologists are still, almost weekly discovering new species. 

 The latter locality is close by the new and favorite summer 

 resorts known as Bay View or Petoskey and Charlevoix. 



At Petoskey and vicinity occur those exquisite coral masses 

 which are so extensively polished and sold to summer tourists. 

 The masses range from the size of a hickory nut to that of a 

 man's head ; but the most common are of the size of the fist. 

 They are shaped somewhat like cakes made in " patty pans." 

 The upper surface is covered with six-sided cells about a 

 quarter of an inch in diameter. A delicately crenulated wall 

 runs around each cell. In the middle of the cell appears to 



