20 KENTUCKY GEOLOGICAL SURVEY. 



brachiopoda, particularly the former, are the prevailing types 

 of animal life. Echinoderms, sponges, mollusks, Crustacea, 

 and coelenterates have many representatives, but are much less 

 abundant, and in some strata are almost wanting. Hence for 

 stratigraphic purposes the bryozoa and the brachiopods are the 

 most important groups. The species of bryozoa are, on the 

 whole, much more limited in vertical range than the brachi- 

 opoda, and hence are the more valuable for close correlation 

 work. They have the disadvantage, however, for practical work 

 that they can seldom be identified without a magnifying glass, 

 and require rather careful discrimination. They look much 

 alike at first glance. For careful work microscopic sections are 

 necessary. 



The bryozoa seem to have been a rather sensitive type of life, 

 changing readily with changing conditions, yet possessed of 

 great race -vitality, for they are abundant even to-day, while 

 the brachiopoda have but few living representatives. However, 

 the suborder of bryozoa most abundant in the Ordovician, the 

 Trepostomata, diminishes greatly at the close of the Ordovician, 

 and at the close of the Paleozoic becomes extinct. On account 

 of the importance of the bryozoa in stratigraphic work in the 

 Cincinnatian series, the paleontologic part of this paper is de- 

 voted to them entirely. 



Mohawkian Series. 



Lexington Group. 



No attempt -is made here to treat this group with any full- 

 ness, as the report of Professor Arthur M. Miller describes ful- 

 ly the development of the Lexington and its subdivisions. 11 

 The formations of the Lexington are mainly limestone, often 

 quite massive. In some parts shale partings are frequent. Fos- 



"The lead and zinc. bearing rocks of Central Kentucky (Ky. Geol. Surv., 

 Bulletin No. 2, 1905). 



