April II, 1878] 



NATURE 



477 



homblende-andeslte {in German Griinstein-trachyt), a compact 

 fine-grained crystalline, more or less vitreous 'rock, containing 

 crystals of oligoclase and hornblende, but no quartz or sanidine. 

 This rock is a good heat-conductor, with a conductivity probably 

 nearly approaching that of ' Calton trap rock. ' 



"The Franzschacht is sunk in rhyolite (a highly siliceous 

 vitreous trachyte), a rock, the conductivity of which would 

 presumably be nearly the same as that of homblende-andesite, 

 probably a little greater. Elements of temperature-disturbance 

 are, however, present in the form of thermal springs, and, 

 possibly, in the proximity of a basaltic cone. This last element 

 of disturbance is, I should imagine, a very doubtful one indeed, 

 although Councillor A. Pech appears to think it of importance. 

 The rate of increase, as deduced from observations in the 

 rhyolite here, was 1° C. for 40'55m,, or about 1° F. for 74 feet. 



"The report brings out strongly the important variations of 

 rock-temperature which may be, and are occasionally, generated 

 by the decomposition of metallic sulphides, a point which I think 

 is here prominently mentioned for the first time." 



At the request of Mr, Lebour, observations have been taken 

 by Mr, Matthew Heckels, Manager of Boldon Colliery, between 

 Newcastle and Sunderland, in holes bored upwards to a distance 

 of ten feet from some of the deepest seams. 



The mine is described as " perfectly dry," and those parts of 

 it in which the observations were made are quite free from 

 currents of air. The surface of the ground is tolerably level, 

 and is ninety-seven feet above Trinity high-water mark. 



Hole No. I is bored up from the roof of the Bensham seam. 

 The thermometer — one of the new slow-action instruments, not 

 self-registering — ^was placed at the end of the hole (so as to be 

 ten feet within the rock) and protected by air-tight plugging. 

 The surrounding strata consist of arenaceous shale, known as 

 "grey metal." The distance of the thermometer from the sur- 

 face of the ground overhead was 1,365 feet. 



The hole had been standing idle for some time when the ther- 

 mometer was inserted, April 5, 1876. The first reading was 

 talcen April 26, and was 75°, the surrounding air being at 75^°, 

 and almost stagnant. The readings were repeated during four 

 consecutive weeks, without change of the indications. 



Hole No. 2 is in the same vertical with No. i, and is bored 

 up (also to the height of ten feet) from a deeper seam— the 

 Hutton seam. The same thermometer was employed, and in 

 the same manner. The surrounding strata consist of a close, 

 compact sandstone known as ' ' hard post. " The distance of the 

 thermometer from the surface of the ground overhead was 1,514 

 feet. Immediately after the drilling of the hole, June 6, 1876, 

 the thermometer was inserted, and on July 4 the first reading 

 was taken, namely, 81°, On July 24 it had fallen to 79^°, and 

 on August I to 79°, Readings taken on August 15 and 29 and 

 September i also showed 79', the surrounding air having never 

 altered from the fixed temperatmre, 78|°, It would therefore 

 appear that the first observation in this hole was 2° too high, 

 owing to the remains of the heat generated in boring, notwith- 

 standing the lapse of four weeks which had intervened. Four 

 readings have since been taken at regular intervals, ending with 

 July, 1877, and the same temperature, 79°, continues to be 

 shown. 



Assuming 48° as the mean annual temperature of the surface, 

 we have the following data for calculating the rate of increase 

 downwards : — 



Surface ... ... ... ... ... 48° 



1,365 feet 75' 



1,514 feet 79° 



For the interval of 149 feet between the two holes we have an 

 increase of 4° F., which is at the rate of 1" F. in 37 feet. 



For the whole depth of 1,514 feet from the surface to the lower 

 hole we have an increase of 31°, which is at the rate of \° F. in 

 49 feet. 



In explanation of the length of time required for the heat of 

 boring to disappear in the second hole, Mr. Heckels remarks 

 that " it required two men sixteen hours with a hand-boring 

 machine to drill this hole, so hard is the stratum." He further 

 says : " The tool by which this hole was bored, on being drawn 

 out, was too hot to allow it being touched with the hand, so that 

 the temperature of the hole, on being finished, must have been 

 considerable ; and no doubt it would be when we consider the 

 immense pressure required to bore holes in such strata as this." 

 With respect to the permanent temperature, 78^°, of the sur- 

 rounding air, Mr. Heckels emarks : ' ' The air of this district is 

 almost stagnant, and what circulation there is will have travelled 



a distanpe of three miles underground ; and hence it may be 

 expected to be itself pretty near the temperature of the rocks 

 through which it is circulating." 



The dryness of the mine, the absence of currents of air, and 

 the great depth render these observations extremely valuable for 

 the purpose which the Committee have in view, and their best 

 thanks are due to Mr. Heckels and the proprietors of the colliery 

 for the trouble and expense which have been incurred in pro- 

 curing them. Observations will shortly be taken in another 

 bore in the same colliery. 



During the past year the first observations have been received 

 from India. They were taken by Mr. H. B. Medlicott, M,A., 

 of the Geological Survey, in bores made in search of coal, and 

 have been published by him in the " Records of the Geological 

 Survey of India," vol, x., part i. The instrument employed 

 was a " protected Negretti " thermometer sent by the secretary 

 of this Committee to Dr, Oldham, the director of the Survey, 

 A Casella- Miller thermometer was used to check the observa- 

 tion?, but was found much less sensitive and steady, and its 

 readings, though placed on record, are therefore left out of 

 account by Mr, Medlicott in his reductions. 



The observations were taken in three bores, at places named 

 Khappa, Manegaon, and Moran; but the observations at 

 Moran were made only four hours after the boring tool had been 

 at work, and the Khappa bore exhibited a strong bubbling, 

 besides other marks of convection. The results obtained at 

 these two bores must therefore be discarded ; but in the Mane- 

 gaon bore everything was favourable for satisfactory observation. 

 *' It was closed on April 24, 1875, so that it had been at rest for 

 twenty months. There is only one guide-pipe ten feet long at 

 the top of the bore, there never having been any pressure of 

 water in the hole. The position is low, and the water had 

 always stood at or near the mouth of the tube. There was no 

 difficulty in removing the plug. The very equable series of 

 temperatures is the natural result of these conditions. The 

 observations were taken in the evening of the 5th and morning 

 of the 6th of December. At 5 p.m. the air-temperature was 

 72°; at 8 P.M., 59°; at 8 A.M., 65°; at ir a.m., 84°. The 

 slight decrease of temperature in the top readings is a good 

 proof of the perfectly tranquil conditions of observation. 

 It is no doubt due to the excess of summer heat not yet 

 abstracted ; and it is apparent that that influence reaches to a 

 considerable depth — quite to sixty feet." The following are the 

 observations : — 



Depth, 

 (eet. 



10 

 20 

 40 

 60 

 80 

 ICX3 



Temperature, 

 Fahr. 



8ri5 

 8i-i 

 81 O 

 81 -o 

 81 -3 

 8i-8 



Depth, 

 feet. 



150 

 200 

 250 

 300 

 310 



Temperature, 

 Fahr. 



827 



83-3 

 84-0 

 84-65 

 8470 



This last observation was in mud, the hole, which had 

 originally a depth of 420 feet, having silted up to such an extent 

 that 310 feet was the lowest depth attainable. The increase 

 from 60 feet downwards is remarkably uniform, and the whole 

 increase from this depth to the lowest reached is 3°7, which is 

 at the rate of 1° F. for 68 feet. 



The elevation of Manegaon is estimated at 1,400 feet. It lies 

 "in an open valley of the Satpuras, traversed by the Dudhi 

 River, south of the wide plains of the Narbada Valley, about half- 

 way between Jabalpur and Iloshungabad, which are 150 miles 

 apart." Jabalpur is 1,351 feet above sea-level, and has a mean 

 annual temperature of 75*2. Iloshungabad is 1,020 feet above 

 sea-level, and has a mean annual temperature of 78*3. 



" The geological conditions of the position are favourable for 

 these observations. The rocks consist of steady alternations, in 

 about equal proportions, of fine softish sandstones, and hard silty 

 clays of the upper Gondwana strata, having a steady dip of about 

 10°. . . Strong trap dykes are frequent in many parts of the 

 stratigraphical basin ; but there are none within a considerable 

 distance of these borings. There are no faults near, nor any 

 rock-features having a known disturbing effect upon the heat- 

 distribution." 



Mention was made in last report (p. 209) of two methods which 

 had been suggested by members of the Committee for plugging 



