42 GEOLOGY OF OHIO. 



flexures become less crowded and less pronounced, until in western Penn- 

 sylvania they no longer constitute the dominant features of the country. 

 They are flattened and reduced until the pitch of the strata falls as low as one 

 or two degrees, and the beds now traverse the summits of the arches with- 

 out any fracture whatever. It has been found by the experience of the last 

 twenty-five years that these unbroken arches are the. main repositories 

 of the oil and gas that have acquired such extraordinary value within this 

 period, especially in Pennsylvania. The further westward the arches are 

 followed, the feebler they are found to be ; consequently, only the lowest 

 of the Pennsylvania series pass into Ohio, But the same law holds be- 

 yond state boundaries; and the folds which are due to the same general 

 cause, that originate and run their entire course in Ohio, are even lower 

 and weaker than the lowest of Pennsylvania. They no longer take an 

 important part in the topography of the regions which they traverse, and 

 they can be detected only by close and continuous series of measurments. 

 Sometimes they are represented only by a suspension of the usual dip, 

 the beds taking a terrace-like arrangement for a small space. They are, 

 however, still found, to some extent, effective in the separation of the 

 contents of the porous rocks of the series involved. Consequently, the 

 driller for oil and gas makes constant inquiry as to the location of the 

 axes or anticlines of eastern Ohio. It is not pleasant to be obliged to an- 

 swer that these important structural lines have not been as yet laid down 

 upon our maps, but this is the fact in regard to them. As already im- 

 plied, the feebler the axes, the greater must be the difficulty in tracing 

 and locating them. Labor enough has been spent on this line of ques- 

 tions to have accurately located all of our anticlines, if they could have 

 been followed with the same ease and certainty with which the arches of 

 western Pennsylvania are traced. But aneroid measurements are not suf- 

 ficient, as a rule, for this sort of work in Ohio. Nothing less than pro- 

 files run by the engineer's level affords a sure basis for the determination 

 of our feeble folds. But the running of such lines across a rough country 

 is expensive and, furthermore, can be done only under careful geological 

 guidance, for the reason that the determination of the strata on which the 

 whole work turns, involves an accurate knowledge of the entire geological 

 section that is concerned. The scale on which it has been possible to 

 carry on field work in Ohio for the last few years has been so very small 

 that it has been out of the question to attempt the determination of many 

 lines by the methods here noted. A careful examination was made by 

 the Survey of the Baltimore and Ohio railroad from Newark east to Bel- 

 laire, to catch, if possible, the arches that cross this road. A like exami- 

 nation was made of the southern poition of the Cleveland, I^orain and 

 Wheeling railway and a less careful examination of the Cleveland and 

 Pittsburg railroad on Yellow Creek. Private surveys have also covered 

 considerable territory in Muskingum, Morgan, Guernsey and Harrison 

 counties, the results of which have been, in part, available to the Survey. 



