Personal and Scientiiic News. 191 
than in the ideally simple earth that has been generally discussed. 
An external shell of 400 miles thickness would not then measure near- 
ly the whole depth to which cooling would penetrate; conduction and 
contraction would be operative nearly from the center to the surface. 
According to one or another of the various admissable postulates as to 
the distribution of internal temperature at the time v/hen the perma- 
nent external cause was found, the amount of surface contraction and 
the depth of the level of no strain will vary. While the physical 
studies of Read, Davison and others in this direction are of great 
importance, it is well that students should bear in mind the fact that 
their conclusions refer to an earth, but not necessarily to the earth. 
Harvard College, Feb., 1890. W. M. Davis. 
PERSONAL AND SCIENTIFIC NEWS. 
The South African gold fields. The rush of popuhition 
to the new gold fields in south Africa still continues. The 
central town of the district, Johannesburg, has sprung up like 
a mushroom from nothing two years ago to a population of 
20,000. Land then almost worthless has increased in value so 
that central lots are selling at £2,500 an acre, while those in 
the suburbs bring £500. The matrix of the gold is all quartz, 
so that crushing is the only means of obtaining the metal. No 
alluvial washings exist. This places the new region and town 
in a very substantial position. Speculation is less uncertain. 
Capital is required and is fast flowing in. The reef is said to 
extend for 100 miles in length and to have considerable breadth. 
Johannesburg is nearly 2,000 miles from the cape of Good 
Hope and bids fair to become the centre of a large English 
community, though not at present within British territory. 
The gold-be'aring deposit consists of conglomerates, a very 
unusual matrix for gold, though occurring also in Nova Scotia, 
where, however the yield is small. The strike of the reef, which 
is double, is nearly east and west, and its dip varies from 
45° to 80°. 
Mud Eruption in Asia. A remarkable eruption took place 
on Aug. 2, 1889, about 40 miles from Erzeroum in Asia Minor. 
The side of the mountain burst open and the village of 
Kantzorik, with 136 of its inhabitants was buried in a torrent 
of mud flowing from the gap. The flood was about five miles 
long by 300 yards wide, and the solid content has been esti- 
mated at between 50,000,000 and 60,000,000 cubic yards. It 
dried and hardened on the top but remained liquid below. The 
surface became deeply crevassed as is that of a glacier. Fine 
dust caused by the fall of masses of rock caused" a rumor that 
a volcanic eruption had taken place, Init there is no evidence of 
anything of this kind. It was in effect a land slip on a vast 
scale. The district consists of Mcsozoic rocks cut and pierced 
