JtnrE 2«, 1B66.] sen
insect is now abundant in Washington, it will scarcely be noticect in any part of the District seventeen years hence. I base this opinion upon a new phase in the cicada bislorj' ; viz., the presence oT the English sparrow. It is the first lime, perhaps, in the history of the world, that Passer domesticns has hnd an opportunity of fuediag npon this particular brood of Cicada Bepteadccim : and so ravenously and persist- ently does this bird pursue its food, that the ground is strewn with the wings of the unfor- tunate cicada wherever these have been at all numerous: so that, considering the numbers of the sjiarrow and their voracity, very few of the cicada will be left long enough to procreate ud perpetuate the species in this District.
��~ THE QEOLOGY OF NATURAL GAS.
The recent introduction of natural gas into geneial use aa a source of heat for industiial and domestic pur[Kises has raised it from the rank of a mere curiosity to one of the earth's mobt valuable treasures.
To the reader unacquainted with the great change natural gas has effected in all indus- tries where it can be obtained, the following quotation fVom an article in MaemiUan's mag- azine for January, written by Mr, Andrew Carnegie, the chief iron master of Fittsbnrgh, will be a revelation: "In the manufacture of glass, of which there is an immense quan- tity made in Pittsburgh, I am informed that gas is north much more than the cost of coal and Its handling, because it improves the quality of the product. One firm in Pittsburgh is al- ready making plate glass of the largest sizes. equal to the best imported French glass, and is enabled to do so by this fuel. In the manu- facture of iron, and especially in that of steel, the qunlity is also improved by the pure new fuel. In our steel-rail mills we have not used a |x>und of coal for more than a year, nor in our iron mills for nearly the same period. The change is a startling one. Where we formerly had ninety firemen at work in one boiler-house, and were using four hundred tons of coal per day. a visitor now walks along the long row of boilers, and sees but one man in attendance. The house being whitewashed, not a sign of the dirty fuel of former days is to be seen ; nor do the stacks emit smoke. In the Union iron- mills our puddlcrs have whitewashed the coal- bunkers belonging to their furnaces. Most of the principal iron and gloss establishments in the city are to-day either using this gas as ftiel, or making preparations to do so. The cost
��of coal is not onlj' saved, but the great cost of firing and handling it ; while the repairs to boilers and grate-bars are much less."
This new fuel, which bids fair to replace coal almost entirely in many of our chief industrial centres, has not received that attention from the geologist which its importance demands. So far as the writer is aware, nothing has been published on the subject which would prore of auy value to those engaged in prospecting for natural gas, and it is the existence of this blank in geological literature that has sug- gested the present article.
Practically all the lai^e gas- wells struck before 1882 were accidentally discovered in boring for oil ; but, when the great value of natural gas as fuel became generally recognized, an eager search began for it at Pitlsbut^h, Wheeling, and many otiier manufacturing cen- tres.
The first explorers assumed that gas could be obtained at one point as well as another, provided the earth be penetrated to a depth sufficiently great ; and it has required the ex- Itenditure of several hundred thousand dollars in useless drilling to convince capitalists of this fallacy which even yet obtains general cnilence among those not interested in successful gas companies.
The writer's study of this subject began in June, 1883, when he was employed by Pitls- bui^h parlies to make a general investigation of the natnral-gas question, with the special object of determining whether or not it was possible to predict the presence or absence of gas from geological structure. In the prosecu- tion of this work, I was aided by a suggestion from Mr. William A. Earsenian of Allegheny, Penn., an oil-o]}erator of many years' ex|)e- rience, who had noticed that the principal gaa- wellsthen known in western Pennsylvania were situated close to where anticlinal axe.s were drawn on the geological maps. From this he inferred there must be some connection between the gas-wells and the anticlines. After visiting all the great gas-wells that had been struck in western Pennsylvania and West Virginia, and carefully examining the geolt^ical surround- ings of each, I found that every one of them was situatctl either directly on, or near, the crown of an anticlinal axis, while wells that had been bored in the synclines on either side furnished little or no gas, but in many cases large quantities of salt water. Further obser- vation showed that the gas-wcUs were confined to a narrow belt, only one-fourth to one mile wide, along the crests of the anlichuai folds. These facts seemed to connect (i,8a i^i't'^jsi:^
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