and the formation of — and Magnesian Rocks. 381 
Albany, are generally such as indicate a shallow sea. To the 
intervention of carbonate of soda is I conceive to be referred the 
origin of all those dolomites which are not accompanied by 
psums, and which make up by far the larger part of the mag- 
nesian limestones; nor will the dolomites thus derived be neces- 
bonates and sea aera er J am sont to ascribe the formation 0 
certain deposits of carbonate of lime which although pera ir 
in fossiliferous formations, are unlike most of their associated 
are often imbedded silicified shells and corals.* It is not per- 
haps easy in all cases to distinguish between such precipitates, 
which may assume a concr maori structure, He on this — 
tion of any known rock, and Mr. J. peasare at her meeting of the 
talline character of the grains composing eo ones in Ohio, as evidence that 
oe were chemical deposits. He however fell into the error of supposing that 
even quartzose conglomerates have origin, while th 
she aid on nd beds in the sax 
al See with 
d. (Daubrée 
e 6 cg i may 
here mention the from the green sand of gave to 
Sauvage 56-0 p.c phon pernit silica mixed with quartz sand and glauco- 
1 
. Maschke as ee sl on cs ner eal <i cage ee ame “ees — “the 
tion or v t 
five par ? this it separates by evapora 
peer ay of concentrated saline solutions in a form insoluble in water. (Jour. fiir 
kt. Chemie, oS 2338.) In these reactions we have a key to the formation of 
aiions deposi 
