PETROLOGICAL ABSTRACTS AND REVIEWS 593 



mineral of this zone is diamond. Under normal conditions the author 

 thinks a relief of pressure would liquify a certain portion of the infra- 

 plutonic rocks which, on being intruded into the higher zones of the 

 earth's crust, would there solidify under less pressure as a normal plu- 

 tonic rock. Only under exceptional circumstances, for example when 

 the isogeotherms are lowered more rapidly than the pressure, will the 

 garnet-rock cool in its infra-plutonic form, to appear later by erosion. 

 The author considers this garnet-shell to be continuous around the 

 earth and potentially liquid, subject to local fusion and the formation of 

 reservoirs wherever there is a reduction of superincumbent pressure. 



Applying this theory to meteorites, he thinks the chondrules, which 

 occur in so many stony varieties, were formerly garnets, and that clif- 

 tonite in the iron meteorites was formerly diamond. 



Fettke, Charles Reinhard. "The Manhattan Schist of South- 

 eastern New York State and Its Associated Igneous Rocks," 

 Ann. N.Y. Acad. Sci., XXIII (1914), 193-260, pis. 8, bibli- 

 ography. 



The Manhattan schist, the youngest of the three crystalline meta- 

 morphic formations which form bed-rock in southeastern New York, 

 occurs in a series of closely folded anticlines and synclines, usually 

 unsymmetrical and in many cases overturned toward the west. The 

 axes of the folds run northeast and southwest and gently dip to the south. 

 The chemical composition and field-relations of the schist show that it 

 is of sedimentary origin, derived from shales, sandstones, and arkoses. 

 These were laid down conformably upon the underlying limestone to a 

 depth of several thousand feet. Later a series of basic rocks — horn- 

 blende- and actinolite-schists of dioritic and gabbroic characteristics, 

 and granodiorite-gneiss (better gneissoid-granodiorite, since it was 

 determined to be of igneous origin) — was intruded in the form of sheets 

 and sills. Now came a period of intense folding accompanied by intru- 

 sions of granite, aplite, and pegmatite. Later there were intruded 

 various basic rocks — norites and pyroxenites of the Cortlandt series, 

 hornblendite near Croton Falls, and other rocks now altered to serpen- 

 tine. The pegmatitic intrusions still continued, for these later basic 

 rocks are cut by them in several places. 



