120 AUTHORS' ABSTRACTS 



sentatives belong properly with the alkali-granites. The most basic 

 rocks represent an undescribed type, so far as the writer is aware, being 

 very basic mica-syenite-porphyries. 



Together with the diabases these rocks form an eruptive assemblage 

 quite similar to that which characterizes Keweenawan time in the upper 

 lake region, nor, since there is in each case the same relationship to a 

 younger unconformable sandstone of upper Cambrian age, and to an 

 older mass of gabbroic intrusives, can they depart widely from them in 

 age. 



Leaving out of the question the older gneisses of somewhat doubt- 

 ful origin, there were three distinct periods of igneous activity in the 

 Adirondack region. The earliest gave rise to gabbros and granites, 

 the next to diabases and syenite-porphyries, the last to bostonites and 

 various basic rocks (camptonites, monchiquites, etc.). Analyses show 

 an astonishing agreement between the acidic rocks of each period on 

 the one hand and the basic rocks on the other. Though a long time 

 interval elapsed between each, magmatic relationship seems not 

 unlikely. 



Accumulating evidence seems to the writer to indicate the possi- 

 bility that three similar periods were characteristic of the entire shore 

 line of the Canadian and Appalachian protaxes, and that such possi- 

 bility should be added to the working hypotheses of all workers in that 

 field. 



(Other Abstracts, Reviews, and Publications deferred to next number.) 



