69 



that it exists wherever the Silurian rocks are exposed, and that here in an 

 altitude of more than 20,000 feet of the earth's crust, representing a period 

 of untold ages, the greatest break in animal life occurred ; but one-fourth 

 of the genera represented in the lower silurian being found in the upper 

 Silurian, while the species are almost entirely new. 



In Ripley county, along Graham creek, this parting is easily determined 

 by means of the abundant and well preserved fossils, but at ]\Iadison this is 

 not the case. Fossils are easily found from the level of the river to a height 

 of 300 feet, where the favistella stillata bed outcrops. Above this for sev- 

 enty-five feet the strata are nearly non- fossiliferous. At three hundred 

 seventy-five feet above the Ohio the "cliff rock" outcrops, which contains 

 characteristic Niagara fossils. 



In 1859 Prof. Richard Owen, after a hasty examination, stated the favis- 

 tella reef to be the limit. A few years later Prof. Eaton discovered tetra- 

 dium fibratum, a Hudson river fossil, six feet higher. Subsequently, Dr. W. 

 J. S. Cornett claimed that he had discovered a 10 i,nch stratum about fifty 

 feet above the favistella reef containing orthis occidentalis and other Hud- 

 son river fossils, and announced this stratum as the last of the lower Si- 

 lurian. 



In 1889 I commenced collecting fossils, being unacquainted with what 

 has been stated just above. Occasionally at the head of ravines I found 

 fossils in fallen rocks which were undescribed in any of my books on pa- 

 laeontology. Some were sent to S. A. Miller, of Cincinnati, who returned 

 them, saying they were new species. This made me eager to ascertain the 

 position from which the rock bearing them came. Mr. John Hammel and 

 I commenced an investigation and discovered that it is situated near the 

 summit of the precipices forming the various falls west of Madieon. Imme- 

 diately above we found a hard, durable salmon-colored stone which, on ac- 

 count of its greater resistance to decomposition, shielded and concealed the 

 stratum beneath. The upper stratum was found to contain certain Niagara 

 fossils, and later investigation has shown that there is an abrupt palfeon- 

 tological break between the two strata, corresponding to the cycles of time 

 when the lower silurian rocks were elevated above the surface of the ocean 

 and subjected to the disintegrating action of the elements. 



By comparing the upper stratum, according to our determination, with 

 that selected by Dr. Cornett at the stone quarry near his residence, they 

 were found to be identical. Hence, to this gentleman belongs the honor of 

 the discovery, our labors simply confirming his conclusion. 



