II. P. Gushing — Age of the Cleveland Shale of Ohio. 583 



as Newberry finally regarded it ; or it may represent a differ- 

 ent formation from either. The Chagrin overlapped on the 

 region from the east; the Cleveland came in from the south 

 and pinches out to the east ; and it seems as though this black- 

 ish shale did likewise ; it increases in thickness westward so 

 far as we have carried it, and it wedges out at Cleveland. Its 

 rate of overlap is much more rapid than that of the Cleveland, 

 which is the chief reason for my present disposition to regard 

 it as a separate formation, separated from the Cleveland by a 

 small break, rather than as a lower, overlapping portion of the 

 Cleveland. That it is a separate formation from, and has 

 nothing to do with, the Chagrin I feel reasonably sure. But 

 I am far from claiming that the matter is settled one way or 

 the other. Though much like the Cleveland lithologically, it 

 can be distinguished from it ; and since it is wholly absent 

 from the type sections of the Cleveland shale, I am calling it 

 the Olmsted shale, from the excellent exposures of it along 

 Rocky river. 



Unless I greatly. mistake, the large collections of fishes which 

 have been made in Lorain county have come from this Olmsted 

 shale, not from the true Cleveland. Certainly this is true of 

 the collections from the lake shore. And in any case this is the 

 shale which Newberry called Huron in the Ohio reports, and 

 re-identified as Cleveland in Monograph xvi. 



Now the point of all this is, does this blackish Olmsted shale 

 keep on increasing in thickness westward, and what thickness 

 does it finally attain ? And what is its thickness along the 

 Huroi river? This is the type locality of the Huron shale. 

 At Cleveland the drill shows a thickness of 1200 feet of shale, 

 Chagrin and so-called Huron, between the Cleveland shale 

 and the Devonian limestones. At Lorain, 25 miles west of 

 Cleveland, there remains less than TOO feet (probably not over 

 600) of this thickness between the Olmsted shale and the 

 limestone. If the same rate of disappearance by overlap con- 

 tinues, there will not be much of this shale series left by the time 

 the Huron river is reached. How much, then, of the so-called 

 Huron shale in Lake county is real Huron, and how much is 

 Olmsted ? The former is older than the Chagrin shale, which 

 is exposed at Cleveland, the latter probably younger and cer- 

 tainly not older. I cannot answer this question as yet. I 

 merely know enough to suggest caution in regard to drawing 

 any conclusions from the supposed age of the Huron shale at 

 the type locality. 1 surmise that much of it is Olmsted : just 

 as I surmise that much of the Ohio shale at Columbus is 

 Olmsted. If so, many of the supposed Huron fishes may not 

 be Huron fishes at all. 



Shales east of Cleveland. — Passing east from Cleveland, the 

 Cleveland shale runs for some 50 miles to the eastward and 

 then seems to pinch out. It occurs on the west side of the 



