Jlficroscopica/ S/udy of Ohio Liitiestoncs. 167 



consisting of broken shell fragments better preserved than 

 any yet seen. Coralline structure is also shown, the lace 

 corals especially. Crinoid stems occur in various shapes, the 

 five-sided form being most common. 



Among all the sections there can be traced a great similarity. 

 The limestone, under the microscope, is seen to be quite uni- 

 form, and confirms the ob.servation made in the quarries that 

 the abundant and predominant forms are brachiopod shells. 

 One section showed the fossil Siylio/a, a pteropod shell, which 

 often forms whole masses of Devonian limestone, but is ver)' 

 rare in Ohio Devonian. This completes the second series, 

 which is characterized by an abundance of fossil life. 



The Silurian and Devonian periods have preserved to us, 

 under favorable conditions, the great chapters of the life 

 history of the past. 



The study of the carboniferous limestones is as yet incom- 

 plete, but a number of new facts are coming to light, and 

 certain limestones long regarded as unfossiliferous are found 

 to contain a variety of fossil forms, only revealed by the 

 microscope. 



