ra) 
TRANSACTIONS OF SECTION C. 789 
that, in accordance with his previously stated hypothesis, by combined physicat 
and chemical action rocks are fused and lava produced within the outer rind of 
the globe of ten miles in thickness. 
6. On the Post-Cambrian Shrinkage of the Globe. Ly J. Locan Lostry, 
F.GS., Professor of Astronomy and Physiography, City of London 
College. 
The author, having previously shown that a shrinkage of the globe sufficient to 
produce the rock-foldings of post-Cambrian times would require an interior tem- 
perature previous to the shrinkage 5,000° F. higher than now,! in the present paper 
gave his reasons for concluding that such a temperature of the interior mass of the 
globe would give a surface temperature that would render impossible those 
geological agencies of erosion and sedimentation which the Cambrian strata show 
to have been in full operation when those rocks were formed. 
Calculations founded on the British Association rate of increase of underground 
temperature, both on the supposition of a solid globe and of’ one with a fused 
interior, showed that with an increase of 5,000° F, the surface temperature would be 
very much above the critical point of water, the existence of which on the surface 
would be thereby rendered impossible. 
It was further shown that if the author’s estimate of the increase of internal 
temperature required is too high, and only 1,000° F. increase be allowed for the 
interior heat in Cambrian times, the surface temperature would even then be quite 
incompatible with known Cambrian conditions. 
The author’s conclusion is that since Cambrian times there has been no appreci- 
able loss of planetary heat, and consequently no appreciable shrinkage of the 
globe; and that therefore another explanation must be found for rock-crushing, 
rock-folding, elevations, and subsidences of land areas, the uprise and issue of 
lava and of seismic phenomena. 
A table was appended showing the temperature of isogeotherms for every mile 
of thickness of an earth-crust of thirty miles, with a base temperature of 3,700° F, 
7. On the Cause of the Bathymetric Limit of Pteropod Ooze. 
By Percy F. Kenna, £.G.S, 
Preliminary.—Two forms of carbonate of lime are known to the mineralogist, 
viz., Aragonite, rhombic, sp. gr. 2°93, H. = 3-5 —4, and Calcite, hexagonal (rhombo- 
hedral), sp. gr. 2°72, H.=2'5-3'5, The former can be prepared artificially by 
precipitation from a fot solution (90° C.), while the latter is precipitated at all 
lower temperatures. Both forms occur in organic structures, and it is found that 
Aragonite structures when deprived of animal matter are opaque, while Calcite 
structures are translucent. There is no perceptible difference in solubility between 
the two mineral species when dealt with in powder or when of inorganic origin ; 
but in porous formations of every geological age it is found that Aragonite shells, 
of whatever thickness, disappear by solution before thin and delicate Calcite shells 
of Foraminifera and Polyzoa are even sensibly affected. It is probable that 
Aragonite is penetrated by extremely slender fibrille of organic matter, whose- 
removal produces the characteristic opacity. 
Solvent action of sea-water,—Sea-water exercises a solyent action upon cal- 
careous bodies, especially upon and about coral reefs and in the profound depths. 
The solvent is almost certainly carbonic acid disengaged from decomposing organic: 
- matter. The ‘Challenger’ observations show that carbonic acid is present in great 
A} 
abundance in the bottom water at great depths ; it is further known that solution 
is rendered much more rapid by the immense pressures prevailing in deep water. 
2 Report of the British Assceiation for the Advancement of Science, Oxford 
Meeting, 1894, p. 649. 
