240 Scientific Intelligence. 
the fallen walls of the pit and old cones within it, material older 
therefore than the lava that surroundsit. He states that according 
to observations of others in November and early January the cone 
had increased in height so as to be one hundred and perhaps two 
hundred feet above the sides of the pit, instead of on a@ level 
nearly, as in early October; moreover the activity in the south- 
west part had increased and portions of the southwest wall had 
fallen in. - J. Dig: 
2. The Origin of Mountain Ranges considered experimen- 
tally, structurally, dynamically, and in relation to their Geologi- 
cal History, by T. Mrettarp Reapz, C.E., F.G.S., etc., 360 pp. 
8vo, with numerous illustrations. London, 1886. (Taylor & 
Francis).-—The chief fact on which Mr. Reade bases his theory of 
the origin of mountains is that of the expansion of rocks by 
increase of heat. From his own numerous trials he arrives at 
1/190,192 as the mean coefficient of expansion for 1° F., which is 
equivalent to 2°77 feet per mile for every 100° F. (which he takes 
at 2°75 feet). The special mean result for various sandstones ar- 
rived at by the author was 1/178,825 ; for marbles, 1/184,797; for 
slates, 1/193,827; for granites, 1/203,322. .Mr. Reade observes 
that as expansion downward and laterally cannot take place, the 
whole is upward; consequently the rise of surface would be 
3X 2°75=8°25 feet nearly. Hence a crust 20 meters thick heated 
1000° F., which would expand in eaeh direction 550 feet (made the 
amount of consequent elevation by Lyell), would rise 1650 feet ; 
and if the total rise went to form a ridge having a base one-tenth 
of the total area heated, the whole height would be 16,500 feet. 
A rising of molten or half-molten rock below would follow the 
rise; and the tension above would cause great fractures and this 
would lead to great denudation. 
Periods of increased heat have alternated with those of dimin- 
ished heat, and thus may have come contractions as well as expan- 
sions, and so alternations in conditions and in catastrophes, in the 
same mountain region. The increase of heat is due to a great 
increase in the thickness of sediments over the region,—the pre- 
liminary stage in mountain making, as first suggested by James 
Hall. This cause produces a rise in isogeothermal lines from 
below ; and through this accession of heat the lower beds become 
most expanded. Thence come uplifts, fractures, flexures, faults, 
volcanic outflows, and the mountain range. The greatest moun- 
tain elevations have taken place in recent times because the 
Tertiary and Cretaceous rocks added vastly to the thickness of 
accumulations over large areas of the earth’s surface. 
Mr. Reade in illustrating his views, and opposing others, appeals 
chiefly to North American rocks for his illustrations and dwells 
especially upon the Appalachians of eastern America, and the 
Great Basin system studied by Powell, Gilbert and others, of 
western, quoting largely from American reports on the subjects. 
As regards the Appalachians the conditions were just what the 
theory requires, if a thickness of 30,000 feet of rock in a sink- 
