1895.] Petrograp hy. 1083 
sandy soils, whose composition is almost identical with that of the com- 
pact rock from which they were derived. 
SiO, TiO, 2 20; Fe,O, FeO CaO MgO Na,O K,O P,O, Ign Total 
Rock 69.33 4.33 3.60 3.21 2.44 2.70 2.67 .10 1.22—99.60 
Soil 65.69 .31 gsr 4.39 2.63 2.64 2.12 2.00 .05 4.70—99.76 
The disintegration processes are not chemical except in so far as 
hydration is chemical, but they are mainly mechanical. 
Formation of Dolomite.—A most important contribution to the 
study of the formation of dolomite is made by M. C. Klement in the 
Bull. Soc. Belge Géol. Paléontol. et Hydrol. After describing the his- 
tory of the theories of dolomite the author calls attention to the fre- 
quent occurrence of dolomite in the form of coral reefs, as observed by 
Dupont in the Devonian, by Richthofen and Mojsisovics in the Trias, and 
by Dana in the recent raised reefs of Metia in the Pacific. He points out 
that while in the chemical experiments that have been made with a 
view of dolomitizing carbonate of lime, calcite has always been operated 
on, the substance of coral has been shown by Sorby to be probably 
aragonite. The author has, therefore, carried out a large series of ex- 
periments on the action of the constituents of sea-water (particularly 
magnesium sulphate) upon aragonite, the results of which are given at 
full length. From these he finds (1) that asolution of magnesium sul- 
phate, in the presence of sodium chloride, and at a temperature of 60° 
C. or more, decomposes aragonite with formation of a magnesium car- 
bonate, the exact composition of which is difficult to determine, owing 
to the impossibility of isolating it from the residual aragonite; (2) 
that this action increases with the rise of temperature, and with the 
concentration of the solution, and is greatly diminished by the absence 
of sodium CES ; @) that — coral is attacked by magnesium 
sulphate j ; and (4) that the lagoons of modern 
coral reefs offered all the conditions of temperature, saturation, 
etc., necessary for the production of magnesium carbonate in the 
manner of experiments, while recognizing therefore, that dolomites 
may have been formed in more ways than one, M. Klement concludes 
that one of the most usual ways in nature has been the action of heated 
and concentrated sea-water in coral lagoons on the aragonite of coral 
and other skeletons, with formation of carbonate of magnesium, which 
is subsequently, perhaps after solidification of the rock, with the 
remaining carbonate of calcium, converted into massive dolomite. 
(Nature, June, 1895.) 
