352 NEW YORK STATE MUSEUM 



these rocks, though the description does not suffice to bring out 

 the cause for this extra acidity. 



No. 3, Kemp's Palmer hill rock, is exceptional for the region in 

 that the feldspar is altered to scapolite, and it falls badly out of 

 the series in several respects, notably in its low magnesia and its 

 excess of potash over soda. 



The rocks from which analyses 6, 7 and 9 were made, were 

 selected to represent the mean and the extreme phases of the 

 syenitic dikes. No. 6 is much more basic than any other of these 

 rocks known in the region, a silica determination of the one which 

 seemed to approach it most closely showing 59.2^. From this 

 figure to the 68.96^ of no. 9 there is apparently no break in the 

 series. 



This basic rock consists essentially of feldspar, a portion of 

 which is microperthite and the remainder albite, biotite, apatite 

 and a little magnetite, these in order constituting 61^, 33^ 

 4^ and .5^ of the rock. Except for the absence of quartz these are 

 the same minerals which characterize the other dikes, thus indi- 

 cating the genetic connection of this rock with the others. 



No. 7 consists of feldspar, largely microperthite, chloritized 

 hornblende, magnetite and quartz, with a little apatite and much 

 hematite stain. There is about lOfo of hornblende and somewhat 

 less than that amount of quartz in the rock, practically all the 

 remainder being feldspar. Except that in most of the dikes the 

 hornblende is replaced by biotite, this is rather closely the average 

 composition of all. 



The rock of column 9 is composed of microperthite, quartz and 

 specular hematite, with exceedingly slight amounts of chlorite and 

 apatite. The feldspar makes a little under 80^, the quartz a little 

 over nfo and the hematite a little over Sfo of the rock. The feld- 

 spar is very typical microperthite or anorthoclase, composed of 

 orthoclase and albite in the proportion of 2 :3. 



The likelihood that the material of these dikes was derived from 

 the same magmatic source as that of the earlier great intrusions 

 is strongly suggested by a comparison of analyses. 



1 



Si02 47.42 



AI2O3 17.34 



Fe^Os 4.91 



FeO 10.22 



2 



3 



4 



5 



6 



46.73 



63.45 



63.02 



68.5 



68.96 



16.66 



18.38 



14.87 



14.69 



15.25 



3.56 



.42 



6.53 



1.34 



3.28 



8.45 



3.56 



none 



3.25 



none 



