REPORT OF THE DIRECTOR AND STATE GEOLOGIST 



The locks of the Dannemora formation are quite varied and yet 

 quite uniform. Nearly every outcrop shows two or more varie- 

 ties of gneiss interbanded with one another. The rocks also 

 differ much in coarseness or fineness of grain from place to place. 

 Yet there are practically only four varieties of gneiss in the dis- 

 trict, which however grade into one another through intermediate 

 varieties. 



The two most abundant kinds of gneiss in the vicinity are a 

 finely granular red gneiss which has the composition of a granite, 

 that is, made up of quartz and microperthitic feldspar with ad- 

 ditional small amounts of either hornblende or biotite or (more 

 rarely) augite, and magnetite; and a black, more gn< issoid rock 

 with the essential make-up of a diorite, that is, composed of horn- 

 blende and a feldspar ranging from oligoclase to labradorite in 

 composition, with magnetite and either biotite or augite in addi- 

 tion. With these are occasional streaks of a gray gneiss com- 

 posed of biotite, hornblende and an acid plagioclase feldspar, 

 quartz being mostly lacking; and gray to red, evenly granular 

 rocks of quartz, orthoclase feldspar and abundant pyroxene which 

 are often called pyroxene granulites. All these gneisses are cut 

 by a later coarse, red granite or granitoid gneiss, which occurs 

 either in small masses cutting across the foliation of the gneiss, 

 or else more intricately cutting it in thin films and sheets which 

 are in general parallel to its foliation. 



sarily show equivalence in time. This term has priority for the Adiron- 

 dack rocks if a new name is to be used. But no one can now show 

 whether the rocks of the two areas are, or are not, equivalent, nor is 

 any one likely to be able to do so in the near future. No one has any 

 idea of the thickness of either series, nor even how many beds of lime- 

 stone there are. There may be just as great a difference between the 

 eastern and western Adirondack rocks in age as between either and the 

 Canadian. There must be a great difference in age between the top and 

 bottom of the series. It seems therefore to the writer more logical to 

 use a name which brings out a universally observed relationship, rather 

 than to inject into an already overburdened literature a new term, based 

 on what is at present a wholly gratuituous supposition. In these old 

 rocks in which fossils are lacking, it is impossible to apply the same 

 fine discriminations as in the f ossiferous rocks, and it would seem to 

 be time enough to apply a new name when non-equivalence is shown 

 to be something more than a mere possibility. 



