184 



SCIENCE. 



[YoL. VI., No. 135. 



Of course it would be rather hazardous for me to 

 say that the American scorpion, described in a former 

 number of Science, was not the young of Eusarcus 

 scorpionis (Grote and Pitt), in as positive language as 

 Mr. Julius Pohlman says it is ; for our knowledge of 

 the embryonic features and development of the Euryp- 

 teridae is yet too little to allow of many positive as- 

 sertions, where not accompanied by absolute evidence. 

 Still I must say that I do not believe it to be the 

 young of that or any other Eurypterid. The form 

 of the limbs, the existence of the nipper-shaped palpus 

 and of an apparently true mandible, resembling so 

 much those of the Scorpion idae, are features which 

 we should scarcely look for in an embryonic or un- 

 developed form of Eurypterus. If Mr. J. Pohlman 

 had seen the photographs of the specimen instead of 

 the rude cut, or had examined the specimen itself, 

 I think he would have expressed a very different 

 opinion. R. P. Whitfield. 



The geology of natural gas. 



I do not wish to enter into a further discussion of 

 the interesting question of the geology of natural 

 gas, in anticipation of the results of a special investi- 

 gation which has just been commenced in the oil and 

 gas regions by Mr. John F. Carll for the State geo- 

 logical survey, but, in reply to Prof. I. C. White's 

 criticism of my letter on this subject, I desire to state 

 a few facts in support of my conclusion, that the 

 'anticlinal theory' alone is insufficient to account 

 for the existence of natural gas, in all localities in 

 the Pennsylvania and adjoining gas regions. In or- 

 der to clearly understand this communication, refer- 

 ence should be made to Science, June 26 and July 17. 



In the first place, it is important to know that the 

 general statements contained both here and in my 

 letter of July 17, refer, not only to all the gas regions 

 of Pennsylvania which, with possibly the exception 

 of the Erie district, are geologically connected with 

 the oil-fields, but also to those other gas localities in 

 New York, Ohio, and West Virginia which are not 

 in the vicinity of producing oil-wells. The facts re- 

 lating to the geology of natural gas, now in the posses- 

 sion of any one geologist, are not sufficiently numerous 

 or connected to permit of the deduction of any ulti- 

 mate theory ; and it is only possible, for the present, 

 to deduce special geotectonic conditions under which 

 natural gas has so far been exploited. Some of these 

 conditions are so varying and apparently antagonistic, 

 that it is only possible to differentiate any one of 

 the general laws controlling the occurrence of nat- 

 ural gas by a comparison of the individual facts 

 obtained from innumerable well-drillings. 



The facts given here will serve to elucidate my pre- 

 vious article, and I hope will prove to be sufficient to 

 clearly define the few conclusions at which I have ar- 

 rived, from field observations extending over a period 

 of ten years, and from numerous studies in conjunc- 

 tion with Mr. Carll, of the results of his surveys, 

 which are more thorough, complete, and valuable 

 than any examinations which have ever been made 

 bearing on the geology of both petroleum and natural 

 gas. 



The genera] structure of the strata drilled through 

 by the gas-wells in the vicinity of Pittsburgh) now 

 considered the most important gas district) is the 

 same as that of the strata in the different parts of the 

 Devonian and carboniferous series pierced by the oil- 

 wells at the Smith's Ferry (.30 miles N. 60° W. from 

 Pittsburg) and the Slippery Rock (34 miles N. 20° 

 W. from Pittsburgh) districts, where in both districts 

 heaw oil is obtained from the base of the coal meas- 



ures, and amber oil from the Berea grit; in the Thorn 

 Creek (25 miles N. 5° E. from Pittsburgh), and south 

 end of the Clarion, Butler, and Armstrong (28 miles 

 N. 20° E. from Pittsburgh) districts, where oil is ob- 

 tained from the Venango (Devonian) sands; and in 

 the Pleasant Unity (30 miles S. 65° E. from Pitts- 

 burgh), Dunlap Creek (31 miles S. 12° E. from Pitts- 

 burgh), Whiteley Creek (45 miles S. from Pittsburgh), 

 and Dunkard Creek (48 miles S. from Pittsburgh) 

 districts, where oil is obtained from the Mahoning 

 sandstone (lower barren coal measures) and overly- 

 ing strata. The discovery of oil at Mount Nebo, about 

 eight miles north-west of Pittsburgh, and the several 

 small oil-wells reported to have been obtained in close 

 proximity to the Washington (Chartiers Creek) gas- 

 wells, together with traces of oil found upon special 

 examination in the gas from wells which are supposed 

 to produce absolutely dry gas (the gas obtained 

 from the Carpenter well on the Daum farm, West- 

 moreland county, was supposed to be free from oil or 

 water: when, however, the gas was confined under a 

 pressure of a hundred and sixty pounds to the square 

 inch, water was precipitated), the existence of natural 

 gas, either in or near all the productive oil-pools, un- 

 der geological and physical conditionssimilar to those 

 found to obtain in what are frequently spoken of as 

 ' natural-gas regions proper,' are all sufficient rea- 

 sons for considering the districts producing either oil 

 or gas exclusively (?) one in a geological sense. 



Gas-wells are not entirely confined to narrow belts 

 (one-fourth to one mile wide) along the crests of an- 

 ticlinal folds, nor are those which have apparently 

 been found in synclines necessarily in the vicinity of 

 subordinate crumples or anticlinal rolls which are so 

 frequently found in extensive basins. The ''dip of 

 the gas-sand and the position of the anticlines and 

 synclines " is the third of the five principal geological 

 and physical conditions, which I have already enum- 

 erated {Science, July 17), which seem to influence the 

 occurrence of natural gas, and in special cases would 

 seem to be the most important consideration. Most 

 of the saddles and basins in western Pennsylvania 

 have a progressive dip along their axial line toward 

 the south-west; and a well, drilled half a mile to the 

 north-west or south-east of a given point on the crest 

 of an anticline, will encounter any given stratum at 

 the same elevation as a well drilled immediately on 

 the crest of the same anticline at a distance south- 

 west from the given point, the distance in each case 

 being dependent upon the intensity of the dip in 

 the three directions. The anticline along which 

 the famous Murraysville gas-wells in Westmoreland 

 county have been drilled is an instance. 



About ten miles north-east of the village of Mur- 

 raysville, two large gas-wells have been obtained 

 about three miles apart (north-west and south-east), 

 one on Beaver Run, the other on Pine Run. The 

 total dip of the Upper Freeport coal-bed, from the 

 Beaver-run well to the Pine-run well, is two hun- 

 dred and fifteen feet, or at the rate of seventy feet 

 per mile toward the north-west. The former well 

 is found in close proximity to the anticlinal axis 

 along which the great Murraysville wells are ob- 

 tained, farther to the south-west; while the latter 

 well is near the synclinal axis. The extension of 

 the general direction of this anticlinal line to the 

 north-east of the Beaver-run well crosses the Cone- 

 maugh River near the mouth of Roaring Run, where a 

 well was drilled, evidently on account of the exist- 

 ence of the anticline at that point; but no gas was 

 found. The Apollo well, about three miles north- 

 east of the Pine-run well, along a line parallel to the 

 structural lines of the district, found no gas. In the 



