Alicroscopical Study of Ohio Liineslones. i6i 



tioii to the waterlinie group, which is regarded by some as 

 fossiliferous, and by others uiifossiliferous. 

 Our Ohio column begins with the 



LOWKR SILURIAN SKRIES. 



The remnants of the old Silurian or Ordovician Sea in Ohio 

 occupy about a dozen counties in the soutluvestern corner of 

 the State. The beds are highly fossiliferous, containing large 

 numbers of brachiopods, lamellibranchs, trilobites and crin- 

 oids, so that the region forms the best collecting ground in 

 the State for the j^aleontologist. This is the oldest formation 

 of the geological scale of the State, and its life and general 

 microscopical character have been studied with greater care 

 and completeness than any other group, but its microscopical 

 characters have never been investigated. 



Selecting carefulh- a dozen slides, and examining them under 

 the microscope, we find revealed to the eye monticuliporoids, 

 with the species iiiaDiiiiuIala and raDwsa especially abundant ; 

 the Trenton tentaculite ; the spiny head shield of acidaspis ; 

 crinoid joints very numerous ; and with these fragments of 

 shells, with their characteristic structure, of these only one 

 was perfect enough for identification — the small Cyclora miiiuta. 



Numerous crystals of calcite or dolomite occur, showing 

 the characteristic rhombohedral cleavage. It is impossible to 

 separate these two minerals under the microscope, but, as this 

 is a magnesian limestone, the crystals might be termed dolo- 

 mite. 



A ver}- fine section of Plilodictya fcncstelliformis w^as ob- 

 served, which did not appear before the grinding, thus show- 

 ing, in a slight way at least, the utility of microscopic exami- 

 nation of rocks. 



The predominant structure consists of shells and coral 

 remains, either entire or broken. These shell fragments, 

 though too small for identification, are yet useful to show the 

 minute shell structure, appearing under a low power as mere 

 dots, but under a high power are resolved into obscure wavy 

 lines and circles. These various structures found show the 

 diversity of life in the old seas, and prove that, while brach- 

 iopods and polyzoans form the greater part of the preserved 



