June 1, 1887.]i 



♦ KNOW^LEDGE ♦ 



177 



lower will be poor, while the part extending beyond the 

 lower will alone be rich. Still more marked and significant 

 are the peculiarities recognised when there are three sand 

 tracts at diflerent depths, for in such cases, while the second 

 is found to be richest where it extends beyond the lowest, 

 and the uppermost richer where it extends beyond the 

 second, the uppermost is richest of all where it extends 

 beyond both the next lower and the lowermost of all. This 

 corresponds exactl}' with what might be expected if the gas 

 rising from organic matter, decomposing under the influence 

 of high temperature, were absoi'bed by the overling sand 

 tracts, wherever the conditions were suitable, the absorption 

 in any given sand tract, of course, diminishing the amount 

 which could give rise to a sand tract above. The signi- 

 ficance of this peculiarity can hardly then be misunder- 

 stood ; we may safely conclude that it has been by this 

 process of distillation, and not in situ, that the oils have 

 been formed in the great oil-sand regions of Pennsylvania 

 and New York. 



It would seem as though the oil had been formed from 

 the condensation of gas rising from the carbonaceous shale 

 lying at greater or less depths below the sands where the oil 

 is found. Such carbonaceous gas would be generated in 

 immense quantities from materials brought into the region 

 of the Appalachian range from various soui'ces and at 

 various times. Large quantities of organic matter were 

 stored in the limestones and shales of the enormously thick 

 beds of the silurian formation, augmented afterwards by the 

 contents of rich carbonaceous deposits during the Lower 

 Devonian age. From these masses of organic matter, sub- 

 mitted at times to high temperatures, and always at immense 

 pressures, deep as they lay below the region of the oil- 

 collecting sands, immense quantities of carbonaceous gas 

 would rise, to be condensed in some regions into oils, but 

 elsewhere to remain as gas at very high pressure, and ready 

 to burst forth with amazing energy whenever an outlet 

 should be found or forced for it. [It is to be observed that 

 for the formation of the oil pools the carbonaceous shales 

 and the sandstone rocks are both in equal degree necessary, 

 the former to produce the oil-gas, the latter to retain it on 

 its way towards the surface, where, unless thus captured, it 

 would escape.] 



It can hardly be doubted, I fear, that the supply both of 

 oil and gas has now been so largely drawn upon that within 

 less than a score of years scarcely any will be left which can 

 be brought at reasonable cost into the market. The 

 boundaries and extent of the oil regions have been deter- 

 mined. All the sands in which oil will ever be foimd in 

 such quantities as to be worth working are known, and 

 have been drilled through in various places. It is saxrcely 

 possible that any new fields will be discovered which will be 

 comparable either in extent or productiveness with those 

 now known. So far back as Januar}' 1883, Professor Lesley 

 pointed out that no petroleum is now being produced in the 

 Devonian rocks, either by the process akin to distillation, 

 described above, or otherwise. What has been stored up in 

 the past, a process whicli probably lasted for millions of 

 years, may be got out. But when these reservoirs are ex- 

 hausted there will be an end of the petroleum supply. 

 "The discovery of a few more pools of two or three millions 

 of barrels each can make little difference." Mr. Carll, 

 whose opinion on the geology of the oil-bearing districts 

 may be regarded as decisive, has come to a similar con- 

 clusion. " There are not at present," he pointed out quite re- 

 cently, " any reasonable grounds for expecting the discovery 

 of new fields which will add to the declining products of 

 the old, so as to enable the output to keep pace with the 

 shipments or consumption." 



The stored petroleum in this region has then been very 



nearly exhausted. In less than a generation, a small part 

 of the population of this continent alone has used up nearly 

 all the valuable stores of energy which had been accumu- 

 lated during millions of years of the geologic past. 



More recent inquiries confirm the conclusions of Professor 

 Lesley and Mr. Carll. The signs of exhaustion in the oil- 

 producing regions can now be clearly recognised. During 

 the last four years there has been a steady diminution in 

 the output, accompanied by an increase in the price per 

 barrel, which nevertheless does not even maintain the 

 nominal annual value of the supply. Mr. Wrigley an- 

 nounced in 1882 that 154,000,000 barrels of oil had already 

 been raised up to the beginning of that year, and expressed 

 the opinion that not more than 96,000,000 barrels remained 

 to be raised. In this last estimate he was undoubtedly mis- 

 taken, for up to the beginning of 1885 no fewer than 

 261,000,000 barrels had been raised, and in the year 1885 

 as many as 21,04:2,041 barrels (nearly 3,000,000 fewer than 

 in 1884) were obtained. But although the estimate in 

 1882 of the quantity of oil still remaining fell far short of 

 the truth, and though we may admit as possible that even 

 now much more oil remains to be put out than the most 

 experienced geologists suppose, the signs of approaching 

 exhaustion are yearly becoming more unmistakable. The 

 expense of bringing the oil to the surface grows greater 

 year by year, and threatens soon to become so great that 

 the profit of working the oil stores will be evanescent. So 

 soon as that state of things is approached, we may be sure 

 that the oilmen's occupation in Pennsylvania and Western 

 New York will be gone. It has been stated that the 

 Japanese, unwilling to let the le;ist fraction of the earth's 

 interior stores be lost, have been known to excavate a 

 vertical shaft to a depth of 600 feet in order to raise a few 

 gallons of oil per day. But in America when the oil mines 

 are so near exhaustion as this, they will be abandoned ; nay, 

 they will be abandoned long before they approach such a 

 condition. With the failure of the oil supply, all the col- 

 lateral branches of industry associated with it will fail too. 



CLOTHES-MOTHS AND THEIR ALLIES. 



By E. A. Butler. 



N a former paper we gave an account of one of 

 the commonest of our clothes-moths. Tinea 

 pellionella ; it now remains to consider the 

 other members of the same genus to which a 

 similar epithet is applicable. And first as to 

 T. biselliella. This is a little ci-eature, some- 

 thing like pelliondla, but usually rather larger 

 and with shining ochreous fore-wings, which are perfectly 

 devoid of spots ; the hind-wings are paler, and the head 

 reddish. Its caterpillar feeds upon various animal substances, 

 such as hair, feathers, wool, itc, and so may occasionally be 

 found in the linings of sofas and chairs, and in mattresses. 

 It is an abundant in.sect, and its habits are similar to those 

 of the before mentioned species, but there is this difference, 

 that the present insect does not, when a caterpillar, weave 

 for itself a coat in which to go on its travels. At the com- 

 mencement of its larval life it is said to feed without any 

 covering by way of protection ; but after a while it finds the 

 necessity of preserving its delicate body from the attacks of 

 its somewhat ill-tempered and aggressive companions, if from 

 nothing else, and therefore constructs a kind of tubular 

 tunnel in which to take shelter. This, however, is fixed to 

 some support, and is thus a shed rather than a garment. 

 It is in this run, too, that the change to the chrysalis takes 

 place ; but then the ends are closed up, and the dormant 



