604 GEOLOGY OF OHIO. 



At the base of the Corniferous Limestone we lose in Ohio all trace 

 of vertebrate existence and must go elsewhere to find any older forms. 

 And even elsewhere the search has not been very well rewarded in so far 

 as it regards the problem of the ancestry of fishes. Though the Upper 

 Silurian strata of Europe have yielded a considerable number yet these 

 differ in structure so far from those of Devonia that comparison is diffi- 

 cult, and direct lineage scarcely probable. Similar fossils were found in 

 1883 in rocks of almost the same age in Pennsylvania *but they furnished 

 no new material for answering the question. The Silurian type is one 

 and the Devonian another and very different and the links are lacking. 



Some hope was raised in 1890 by a reported discovery of fish-fossils 

 in Colorado, in Ordovician (Lower Silurian) strata, f But the results 

 thus far have not realized the expectation, and the evidence is far from 

 sufficient to bridge for the palaeontologist the enormous time-interval 

 or to outweigh logically the immense improbability that creatures so 

 comparatively high existed at a date so remote. Time will show, but at 

 present we must admit that the origin of the vertebrates is shrouded in 

 mystery. 



Possibly the imperfection of the geological record is sufficient to 

 account for the whole of this great gap in evolutionary history. So much 

 destruction and relaying of the rocks has taken place that the old family 

 record of the fishes may have been altogether destroyed, or if still in 

 existence it may be buried deep beyond our reach. But if we may trust 

 that the future will be as the past there is ample ground to hope that 

 when the yet unexamined parts of the globe are studied by geologists, or 

 even when a more thorough investigation shall be made of regions com- 

 paratively well known, we shall come upon precious fossils that will be 

 eloquent to the ear of science regarding the ancestry of the long extinct 

 but deeply interesting residents of our State before it had been raised 

 above the waters of the primaeval ocean. 



The discoveries of the Rev. H. Hertzer were made known to the 

 world b}^ Dr. Newberry at the meeting of the American Association at 

 Buffalo, in 1866, and excited considerable interest. This was the 

 greater because the beds in which they were found had been previously 

 regarded as altogether barren. In like manner the Cleveland Shale where 

 Dr. Clark and Mr. Terrell have since made discoveries rivaling those of 

 Mr. Hertzer in all except date, was looked on by geologists as barren 

 ground. It is so generally, but the fact that these usually unfossiliferous 

 beds prove in certain places so wonderfully productive should encourage 

 all to search well a stratum before condemning it. 



Accounts of the fossil fish fauna of the Ohio Shales have been 

 published in three places — in the first and second volumes of the " Palae- 

 ontology of Ohio," in the "Monograph of the Fossil Fishes of North 



* E. W. Claypole on Palaeaspis in Quart. Jour. Geol. Soc. Lond.. 1884 and '91. 

 t C. D. Walcott in Bulletin of Geol. Soc. of America, 1892, p. 153. 



