512 B. K. EMERSON 



as a growth of secondary albite in steam holes. This sug- 

 gestion depends upon a comparison with material of excep- 

 tional excellence from Cheapside where the whole process could 

 be followed and where the perfect crystals of albite could be 

 isolated and determined in heavy fluid. The chemical differ- 

 ences between the two rocks are many, as may be seen by com- 

 paring the analyses given above. In the matter of Si0 3 and 

 A1 2 3 , the Holyokeite is intermediate between the keratophyr 

 of Hovey and the normal diabase. 



The minute quantity of iron (not enough to satisfy the S and 

 Ti0 2 ) and magnesia, show that there can scarcely have been a 

 trace of augite or sahlite present in the Holyokeite, while the 

 keratophyr may have contained much bisilicate. Finally the 

 discrepancy in the CaO is decided, even after saturating the 

 C0 2 , and would demand, considering also the smaller amount 

 of Si0 3 , a somewhat larger proportion of anorthite in the Holy- 

 okeite, while the larger amount of K 2 would demand for it a 

 greater amount of orthoclase or anorthoclase. 



The Holyokeite may then be looked upon as representing a 

 limiting form of the diabase series where the bisilicates are 

 wholly wanting. 



B. K. Emerson. 



