888 GEOLOGY OF OHIO. 



and follow them, and practical men in search of ore and coal, have long 

 since learned their value. The reasons for their selection are obvious. 

 Limestones are more individualized than any other strata with which 

 they are associated. They differ from each other in sti jcture, in color, 

 in the presence or absence of fossilr", and to some extent in the kinds of 

 fossils when any are present. They are generally slow to decay, and 

 thus their outcrops are marked in all natural and artificial sections. 

 When they chince to weather easily, they give rise to soils aj character- 

 istic and as easily recognized as the limestones themselves. 



A. LIMESTONES OF THE HANGING HOCK DISTRICT. 



There are six principal limeston? horizons in the Hanging Pock Dis- 

 trict. Five of them stretch through the whole field, and furnish the 

 means of establishing the strati graphical order of every portion of it. 

 They are named as follows, being numbered in ascending order, 



6. Ames or Crinoidal Limestoae. 



5. Cambridge or (locally) Black LimestoDe. 



4. Shawnee or Bufif Limestoae. 



3. HaDging Rock or Gray Limestone. 



2. Zoar or Blue Limestone. 



1. Maxville or (locally) White Limestone. 



The lowermost stratum or the Maxville, is very much less extended 

 than the re-t. It is shown indeed only in isolated patches, and much 

 remains to be learned of its development in the district. While it can- 

 not be claimed as a conspicuous or steady horizon, yet in such portions 

 of the field as it occupies, it serves a very useful purpose in establishing 

 the true order and system of the Coil Measures. 



These several limestone horizons are separated from each other by ap- 

 proximately equal intervals, which vary, however, in different parts of 

 the field, being generally increased as they are followed sjuthward. In 

 the Hocking Valley, the intervals are about one hundred feet. Thus 

 the distance from the Maxville Limestone to the Zoar, ranges from one hun- 

 dred to one hundred and thirty -five feet. Nobetteravfragecanbegivenfor 

 the interval between the Blue Limestone and the Gray (Hanging Rock) 

 Limestones than one hundred feet. Again, the Shawnee or Buff Lime- 

 stone lies one hundred to one hundred and ten feet above the Gray. The 

 Cambridge is about one hundred feet above the Shawnee and, finallj', the 

 Ames ranges between eighty-five and one hundredandtwenty feet above 

 the Cambridge. In southern Vinton county, the interval between the 

 Maxville and the Blue Limestone is a little less than that already given 

 —viz., ninety feet. From the Blue Limestone to the Gray, the distance 

 hasbeen increased to one hundred and twenty or one hundred and forty feet> 



