BA S. &. EMMONS 
‘ably carried on, have been recently extended by the experience 
of the Lake Superior mines, where the new shaft at the Calumet 
and Hecla mine is down below 4700 feet and destined to go to 
‘5000. In this case, however, conditions are unusually favorable, 
for the increment of temperature with depth is, according toarecent 
statement of A. Agassiz,’ only 1° in 223 feet, or 79° at the bot- 
‘tom of the present shaft. In South Africa the increment as deter- 
mined by Hamilton Smith is 1° in every 82 feet, which wouid 
produce a temperature of 100° at 3000 feet. This increment, 
‘though below the average, is, there is reason to believe, somewhat 
-overestimated ; more recent estimates make it less than 1° for 
-every 100 feet, which would give only 108° (F) at 4000 feet. 
Production, Past and Future —In conclusion it may be of inter- 
-est to consider some of the figures showing the gold production of 
‘this remarkable region. 
Its output for 1894 was gold to the value of 47,800,000 and 
ifor 1895 it is estimated to reach nearly 48,750,000. Hatch esti- 
mates that by 1900 the annual output will be over £20,000,000. 
‘Up to July 1895 it had already produced £26,670,539. Esti- 
mates of the available supply of gold in the central district of 
‘the Rand with its eleven and one-half miles of outcrop are given 
.as follows: 
By Hamilton Smith - - - - - £325,000,000 
“ Bergrath Schmeisser - - - - - 346,000,000 
« F. H. Hatch - - - - - - 382,000,000 
As these estimates have been arrived at independently and by 
somewhat different methods, Hatch allowing a greater depth for 
profitable working than the others, their slight difference is rather 
remarkable. Hatch further estimates a probable product for the 
whole region, including outlying districts, of 4£700,000,000, of 
\which £200,000,000 will be profit. This amount is greater than 
ithe product of the whole United States up to date. 
S. F. Emmons. 
‘t Am. Jour..Sci,, VoL L, Dec. 1895, p. 503. 
