578 THE JOURNAL OF GEOLOGY. 



closely adjacent points. The law that, apart from volatile con- 

 stituents, the total chemical composition remains unchanged is 

 true not only of the rocks in bulk, but of any individual cubic 

 inch of the rocks. This might be followed out into various 

 corollaries, of which I note only one, viz., that the greatest variety 

 of metamorphic minerals is to be found in rocks which were the 

 most heterogeneous prior to metamorphism. Such rocks are 

 breccias and fault-breccias, etc., and especially basic igneous 

 rocks more or less weathered before being metamorphosed. 



Alfred Harker. 

 Cambridge, England. 



