TRIASSIC IGNEOUS ROCKS NEAR GETTYSBURG 57 



places vesicular and having glassy ground-mass; (9) olivine basalt, dense 

 black variety, with abundant olivine. 



Presented in abstract extemporaneously by both authors. 



DESERT BEQOL1TH AND ITS GENETIC RELATIONS TO MAXIMUM EPIROT1V 



DEPOSITION 



BY CHAJJLES KEYES 



(Abstract) 



It was remarked by many who listened to the admirable illustrated lecture 

 on the "Characteristics of Egyptian deserts," given by Dr. W. F. Hume before 

 the meeting of the Twelfth International Geological Congress in 1913, that it 

 was a very great surprise to learn that arid lands were so dominantly bare- 

 rock plains rather than rolling sand wastes, or tracts deeply mantled by rock 

 debris, as so commonly regarded. That the mantle of decayed rock materials 

 which so widely distinguished most pluvial lands of the globe and which is so 

 aptly denominated the regolith should appear to be so largely wanting in this 

 most famous and typical of deserts was a fact that was directly ascribed to 

 the peculiarities of arid land depletion. 



The recognition of the prevalency of bedrock surfaces over broad tracts does 

 not preclude the existence of frequent and often extensive accumulations of 

 rock- waste in the deserts. Enormous amounts of these soil materials are 

 manifestly not only constantly moved about over wide areas of the arid 

 country, but they are directly exported far beyond desert confines. The areas 

 of greatest accumulation of continental or epirotic deposits appear to have a 

 close genetic relation to the areas of greatest arid deflation. Concrete illus- 

 trations are drawn from four continents. " 



Presented by title in the absence of the author. 



ORIGIN OF FOLIATION IN THE PREGAMBRIAN ROCKS OF NORTHERN NEW 



YORK 



BY WILLIAM J. MILLER 



(Abstract) 



It has been generally assumed that the Adirondack Precambrian rocks, in- 

 cluding the Grenville strata and the syenite-granite intrusive series, have been 

 severely compressed and folded as well as thoroughly metamorphosed and 

 foliated by the compression. 



Evidence will be presented to show that the Grenville strata have never 

 been highly folded or severely compressed. Various broad Grenville belts are 

 known to be only very slightly folded, while many masses, large and small. 

 are merely tilted or domed at various angles, though some local contortions 

 do occur. These structural relations are best explained as having been the 

 result of slow irregular up welling of the more or less plastic magmas (prob- 

 ably under very moderate compression), whereby the Grenville strata, pre- 

 viously deformed little or none at all, were broken up, tilted, and lifted or 

 domed. Some bodies of strata, caught between batholithic magmas, were 

 locally squeezed or contorted. 



