448 GKANITE AlfD DIABASE AT SOREL POINT. [Aug. 1899^ 



Discussion. 



Prof. SoLLAs remarked that, through the kindness of the Author^ 

 he had been able to examine the slices of the rocks described under 

 the microscope, and had recognized some of the characteristic effects 

 which result from the action of a fused rOck on one previously 

 consolidated : the phenomena were much more striking in hand- 

 specimens than in microscopic preparations, and in these enquiries 

 the field-evidence was of the first importance. It was natural to 

 regard the hornblende and biotite surrounding augite as products of 

 the interactions of the magma on a xenolith ; but another possibility 

 should be borne in mind, for the three minerals might be excreted 

 in this order from a homogeneous magma as a result of increasing 

 acidity or changes in pressure and temperature. Evidence was 

 still needed to decide whether the associated hornblende and biotite 

 were derived directly from the magma, or resulted from corrosion 

 of included augite. 



The Author thanked the Society for the reception accorded ta 

 his paper, and briefly replied to the question put by Prof. Sollas,. 

 saying that the production of biotite from augite in these Jersey 

 rocks principally depended on the extent of the mixture with the 

 granite -magma rather than on questions of temperature and 

 pressure, pointing out that this was clearly shown by specimens on 

 the table. 



