Geology and Mineralogy. 825 
turns per second, the radius of measurement from fifteen to — 
feet, and the distance between the mirrors 500 feet. The displac 
3, or about 
Foucault. The mean of ten determinations for the velocity of 
light in air was 186,508 feet, the extremes being 184,500 and 
188,820. The author expresses the hope of being able, under 
more favorable conditions, to obtain the true result within a few 
iles.— (Amer. Assoc. Adv. Science, St. Louis meeting, 1878.) 
II. GeoLtogy AND MINERALOGY. 
1. Note on Mountain-making by the Contraction of the 
Earth's crust ; by J. D. Dawa. —A metho ad of reproducing on a 
sults, which he has pe eenis represent foldings, faultings and 
crushings that look much like some of the effects in the world of 
rocks, 
Mr. H. F. Walling, of Cambridge, in a —_ on the relation 
of adhesion to horizontal pressure in yee n dynamics, read 
before the American Association at St. Louis in August, 1878, and 
— recently, suggested, still tise essentially the same 
mo experimentin 
There are two general facts with regard to actual mountain- 
making that are in accordance with the results which the 
aeiroar ye affor 
1.) Conmetidei in the earth’s crust from cooling must have gone 
sturban 
beyond those from gentle oscillations. Geology has found that, 
for North America, from the Atlantic south of New York to the 
k Mouzisélen and as the facts now stand, to the Pacific, 
there was but one mountain-making epoch between the close of 
beginni 
for the larger part of the broad continent, at least three; fone 4 of 
all geological time after the Archean—amounting to seventy-five 
millions of years, if the whole covered one 
uw 
During all that long time the sedimentary deposits were slowly 
thickening over the underlying crust, il lay like the clay over 
