4 Journal of the Mitchell Society [Septeinher 



4. There are two crests during the year, April-May and Sep- 

 tember-October, due to a tremendous increase of individuals belonging 

 to only ojie or two species rather than as might be expected to a gen- 

 eral increase in all species represented. 



5. There seems to be a definite relation between temperature and 

 number of organisms, the optimum lying between 46° and 55° F. 



6. There is a noteworthy absence of Copcpods certainly due to 

 some error in the method of collection. 



7. Neither ''count" nor "volume" gives an absolutely true in- 

 dication of food available. These two in connection with "incinera- 

 tion" would probably give a more correct idea. 



239th Meeting— February 10, 1920 

 F. P. Venarle — The Chemistry of Zirconium. 



This paper will be published in full in this Journal in a later 

 number. 



W. F. Prouty — Notes on the Geology of a Portion of Clay County, 

 Alabama. 



The fundamental or metamorphic rocks of Clay County, Alabama, 

 have been generally considered of Precambrian age. There is nothing 

 published concerning the age of the associated intrusives. Dr. Smith, 

 of the University of Alabama, has demonstrated the Carboniferous 

 age of a small area in the phyllites of western Clay County. The 

 speaker has recently widely extended, in the phyllite belt, the area 

 of known Carboniferous rocks and has demonstrated the post Car- 

 boniferous age of the belt of green schists which everywhere separate 

 the phyllites on the west from the mica schists on the east. 



The workable flake graphite ores or the mica schist belt are shown 

 to be of epigenetic origin and the association of the ores with the more 

 quartzitic and coarse-grained, originally sedimentary beds, leads to 

 the conclusion that the graphitic ores resulted from the metamorphism 

 of petroliferous strata. 



240th Meeting — March 9, 1920 

 J. F. Dashiell — Double Habit Formation by Animals, Children, and 

 Adults. 



The problem approached was that as to the relative efficiency of 

 learning two habits by practicing them alternately (the Alternate 



