ON UNDERGROUND TEMPERATURE. 21 



depth was due to the difference of temperature of the surface-water which 

 soaked in through the limestone in the two cases. As regards the tempera- 

 tures at depths exceeding 200 feet, it would appear that, in times of compa- 

 rative drought (as in the first set), the heat of the soil at the greater depths 

 has time to produce a little augmentation in the temperature of the water 

 before it soaks away. 



This shaft is obviously not adapted for giving any information as to the 

 rate of increase downwards. Collecting the best determinations from the 

 other shafts we have : — 



Depth of Temperature. Calculated 



thermometer. Fahr, increase, 



ft. „ „ ft. 



Gin-Hill Shaft 400 51-3 1 in 66-6 



High Underground Engine 857 65-7 1 in 40 



Slitt Mine 660 65-1 1 in 33-5 



Mr. Burns considers that little or no weight should be attached to the first 

 of these determinations, as a pumping-engine was working in a neighbouring 

 shaft communicating with it at the time when the observations were taken. 

 The jump of 2° in descending from 340 to 390 feet also renders the inter- 

 pretation of these observations difficult. 



The closeness of the temperatures in the other two shafts, at depths differ- 

 ing by about 200 feet, suggests the idea that they are both fed by the same 

 spring, and that the temperatures indicated are the temperature of the origin 

 of the spring slightly modified by the different temperatures of the strata 

 through which it has passed ; but their positions appear to render this im- 

 possible. 



Mr. Burns's opinion from all the observations is that the mean rate of in- 

 crease downwards at Allenheads is about 1° in 35 feet ; but this cannot at 

 present be held as proved. 



The strata consist mainly of alternate beds of sandstone and shale, with a 

 few beds of limestone intermixed. In Slitt mine there is also a bed of 

 basalt 158 feet thick, overlying the vein of fluor-spar in which the workings 

 are carried on, the workings being 55 feet down in this vein. 



Preparations are being made for taking observations in the dry part of the 

 mines, by making shallow bores at different levels, inserting the thermometer, 

 plugging up the hole for a few days, and then reading. 



Another gentleman connected with H.M. Geological Survey, Mr. R. L. 

 lack, has taken observations in a bore at Crawriggs, Kirkintilloch, near 

 Cilasgow. They were taken on the 29th November 1870, the temperature 

 of the air being 34°. The surface of the water in the bore was 6 feet below 

 the surface of the ground, the latter being 200 feet above sea-level. The 

 Poilowing were the observations : — 



Depth from surface Time of lowering lime of withdrawing Temperature. 



of ground. thermometer. thermometer. Fahr. 



feet. h m h m o 



50 12 52P.M 1 7p.m 47 



100 1 10 „ 1 28 „ 48| 



150 1 33 „ 1 52 „ 49| 



200 1 58 „ 2 14 „ 50 



250 2 22 „ 2 43 „ 50 



300 3 15 „ 3 34 „ 50| 



350 3 40 „ 3 50 „ 51 



A few feet below 350 feet an obstruction in the bore prevented further 



