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POPULAR SCIENCE REVIEW. 
This was the result of soundings taken with every possible 
difficulty and liable to every possible error, and of the extremely 
lively imaginations of the physical geographers of the day. But 
Laplace showed that the depth of the sea is a small fraction of the 
difference of the polar and equatorial axes of the globe, and of 
course his deductions did not relate in any way to measurements 
by soundings. It was a remarkable statement, and has been en- 
hanced in value by the deep-sea soundings of late years. Taking 
the difference of the axes to be, in round numbers, 26 miles, 
the average depth of the great ocean is from 2000, 2400, to the 
extreme of 3000 fathoms, the middle number being the pro- 
bable correct average. This gives a depth of nearly three miles 
to the ocean ; and it is rather under one ninth of the standard 
mentioned. 
According to Laplace, the oceans occupy irregularities of 
the surface of the earth ; and mountains, table-lands, and the 
deep valleys, may be considered irregularities when curvature of 
strata, and great anticlinal and synclinal axes are to be seen 
amongst them. The depth of the bases of mountains, calcu- 
lated from the direction of the downward curvatures of the 
lowest strata and the possible depth of the strata beneath the 
sea, gleaned from the dip of coast-line strata, appear to be 
enormous, and especially to those observers who are untrained. 
But the distinguished mathematician stated as his opinion 
that the irregularities of the surface of the earth and the agents 
which have to do with them, are at, and act at, a very slight 
depth below the surface. That is to say, relatively to the great 
bulk of the globe and its diameter, the space immediately 
beneath the surface, which has been affected by internal move- 
ments during the ages since the present irregularities have 
existed, is small. The depth of the earthquake focus, of the 
hypothetical volcanic reservoirs, and of the movement resulting 
in tangential thrusts sufficient to produce the grandest oceanic 
and continental geosvnclinals and geanticlinals, or the minor 
anticlinoria and synclinoria of mountain-chains is slight, ac- 
cording to Laplace, writing in the second decade of this century. 
The great globe is quiescent within, and any energy still 
lingering on, is very superficial, or is antagonized by the enor- 
mous internal density of the mass. The energy is heat, and 
that was of course acknowledged by Laplace. The amount of 
knowledge of stratigraphical geology was not inconsiderable in 
his day, and the relations of the intrusive to the sedimentary 
rocks were understood ; moreover, there was a belief in the 
primitive nature of granites and such highly crystalline rocks. 
But these and their great curvatures must have all appeared 
like filmy wavelets on the vast globe, to the great mathematician. 
It is doubtful, however, whether this was common knowledge, 
