38 annals new york academy of sciences 



Conclusions 



In review, then, magnesia, in hydrated or carbonated condition, and 

 deweylite and sepiolite, in colloid form, have always been the only mag- 

 nesian derivatives from laterite, with tendency to early migration and 

 transport, in virtue of their solubility. 



Antigorite and talc, on the other hand, crystalline and never colloid, 

 have merely served as insoluble fixatives to harden and record the trans- 

 formations of their mobile and protean predecessors. Chr\'sotile is but a 

 pseudo-fibrous variety of antigorite — in fact, a pseudomorph in antigorite 

 after a pseudomorph in deweylite after nemalite, the fibrous form of 

 brucite. 



To the list of rock-making minerals, brucite, deweylite and sepiolite 

 need to be added as important accessories. 



The evidences in confirmation of these views from field observations, 

 optical examinations, etc., together with a review of the literature of 

 brucite, serpentine, antigorite, and the hydrous magnesian minerals, have 

 been gathered for presentation in a separate monograph. 



Department of Geology, 

 Columbia University. 



