PETROGRAPHICAL PROVINCE OF ESSEX COUNTY 1 07 



of Arran it is easy to explain this by assuming that the first- 

 formed dike cracked down its center, and that this crack was 

 filled by a later injection, which, cooling rapidly, solidified as 

 aplite. This is not the place to enter into a discussion of the 

 subject, but it may be said that in view of the facts noted above, 

 the similarity in chemical composition of the two portions, and 

 for other reasons, this explanation does not seem to be the cor- 

 rect one, and we are forced to conclude that the dike is due to 

 only one injection. In this case the coarser crystallization at 

 the borders may be due, as Professor Iddings has suggested to 

 me, to the presence of mineralizers derived from the surround- 

 ing granite, or, as seems to me more probable, to certain peculiar 

 physical and chemical conditions which I hope to explain in 

 another place. 



1 II III IV 



Si0 2 - 77-49 76.44 77-H 71 '.61 



Ti0 2 - - - - 0.25 0.37 0.29 0.25 



AKO3 - 11.89 I2 -95 12,24 H-94 



Fe 2 3 - - 0.34 0.19 0.29 0.55 



FeO - - 1. 12 0.89 1.04 0.87 



MnO - - - trace trace trace trace 



MgO - - - 0.09 trace 0.06 trace 



CaO -. - - 0.45 0.15 0.35 0.31 



Na 2 - - - 4.58 4-76 4-64 3-8o 



K 2 - - - 4-26 4.95 4-47 4.98 



H 2 0(no°) - - - .... .... .... trace 



H 2 (ignit.) - 0.16 0.09 0.14 0.23 



100.63 100.79 100.66 100.54 



I. Aplite. Border of Dike. Bass Rocks. H. S. Washington anal. 



II. Aplite. Center of Dike. Bass Rocks. H. S. Washington anal. 



III. Aplite. Composition of whole dike, two parts of I, one part of II. 



IV. Granite. Rockport. H. S. Washington anal. Jour. Geol., VI, p. 793, 1898. 



Analyses were made both of the border and of the center and 

 are given above in I and II. The composition of the dike as 

 a whole, calculated from two parts of I and one part of II, is 

 given in III. The two parts of the dike are seen to be sensibly 

 identical in composition, the border with a little more silica, 

 lime and magnesia, and a little less alumina and alkalies. The 



