Microscopjcal Study of Ohio /Jiiicsfotics. 165 



remnant of an old isolated sea basin, which slowly evaporated. 

 The water, becoming salty and bitter, would destroy all life 

 which happened to be present, and on the bottom of this 

 inland sea would be deposited a dolomitic limestone, but no 

 true carbonate, so that all traces of life would be destroyed. 



In 1880, some blocks of this limestone were polished for 

 the National Museum at Washington, and it was stated that 

 "one polished upon the .surface parallel to the plane of strati- 

 fication showed a fossil bryozoan, and thus proved it was 

 fossiliferous." 



This structure does resemble somewhat a fossil, l)ut Mr. 

 C. D. Walcott, paleontologist of the IT. S. Survey, could see in 

 it no proof for calling the limestone fossiliferous. In twent)'- 

 five sections of this stone, taken from different parts of the 

 series, I could find no distinct fossil structure. 



The rock is compact, containing numerous black lines of 

 bituminous matter, which simulate coralline structure, and all 

 very confusing. With a little imagination one can trace out 

 hydrocorallincs and even tube and radiating structure of Ca:n- 

 ostroma, but yet there is nothing definite — nothing that can 

 be regarded as fossil .structure beyond doubt. The bitumen 

 has a peculiar regular parallel and radial arrangement, and it 

 suggests that perhaps there is a replacement of the old hydro- 

 coralline mass by bitumen, so that we have, as it were, a 

 bituminous cast. 



After careful study and thought, it seems to me that this sea 

 must have contained a considerable amount of life, but that 

 this basin was cut off from the main part, then, by its evapo- 

 ration, destroyed the life ; but the limestone was deposited as 

 a carbonate, soon to be replaced by the various magnesian 

 salts, so that the fossil shell and coral were soon replaced, and 

 only casts remained ; then, by consolidation through pressure, 

 even these casts were destroyed. This pressure is shown by 

 occurrence of small pressure columns in the limestone. We 

 are forced, then, to say that the Heldober^ liiucslonc of Ohio 

 is very sparingly fossiliferous, even in microscopic sections, 

 but we can not say the Helderberg sea in Ohio was unthoul life. 



The last great limestone we find in the Ohio scale is the 



