504 REVIEWS 



differences in color of the magnesite or from variations of amounts of 

 serpentine and other minerals present. The strike of the bands and 

 lenses is parallel to that of the Grenville sediments. The deposits 

 have been intensely faulted and crumpled and probably the lenticular 

 structure is the result of deformation. The mode of occurrence of the 

 following minerals associated with the deposits is described: magnesite, 

 serpentine, dolomite, diopside, phlogopite, quartz, talc, pyrite, sphalerite, 

 magnetite, and graphite. 



The three methods of origin for magnesite deposits are: (i) deposits 

 formed by the decomposition of serpentine, (2) sedimentary deposits, 

 (3) deposits formed by the replacement of limestone. The Grenville 

 deposits are thought to have been formed by the replacement of lime- 

 stone. Silication of limestone to diopside and phlogopite is very 

 common along the contacts of limestone and igneous rocks in this region 

 and the igneous rocks are very close to these particular deposits. The 

 writer summarizes the method of origin: "The probable order of events 

 by which the magnesite deposits of the Grenville district were formed 

 was as follows: (i) silication of the limestone to diopside and the forma- 

 tion of phlogopite in places, (2) formation of serpentine in places, (3) 

 replacement of Hmestone by dolomite, (4) replacement of dolomite by 

 magnesite, and (5) the alteration of diopside to serpentine." 



Chapter iv is a detailed description of the properties and gives 

 tabulated descriptions of many magnesite samples with the percentage 

 of CaO. While dolomite and magnesite are very intimately inter- 

 mingled, yet by 1916 development work had proved the presence of 

 686,900 tons of magnesite containing less than 12 per cent CaO and 

 483,700 tons containing over 12 per cent CaO. 



Map 1680 issued in 1919 shows in detail the geology of a portion of 

 the township surrounding the deposits. 



J.F.W. 



Pleistocene Marine Submergence of the Hudson, Champlain and 



St. Lawrence Valleys. By Herman L. Fairchild. New York 



State Museum Bulletins, Nos. 209, 210, Albany, N.Y., 1919. 



Pp. 76, pis. 25. 



This is the closing paper by Professor Fairchild on the glacial and 



post-glacial waters of New York State and in it he discusses the proof 



and extent of the marine submergence following the retreat of Wisconsin 



glacial ice from northern New York State. The stratified clay and 



