118 THE GEOLOGY OF THE .MELDOX Y ALLEYS, [vol. lxXV, 



demand inclusion amons; the efficient agents of erosion and 

 denudation. 



He was much interested in Sir Douglas Mawson's description of 

 the large crystals of chiastolite, which in Australia presented the 

 same peculiarities as the small Meldon crystals. While the prism- 

 faces would be favourably placed for securing preferential supplies- 

 of material when once the cross form had been established, he 

 could not yet grasp the efficiency of this preferential supply in 

 initiating the form. In the normal prism it would appear that 

 the prism-angle had the greatest available adjacent area of supply. 

 But the suggestion was new to him, and he might have overlooked 

 some essential feature. 



The President and other speakers had referred to instances of 

 intrusive dykes formerly mapped as ash. That possibility, in the 

 absence of rather detailed field-work, was undoubted ; there seemed 

 at present to be some reaction against the tendency to identify as- 

 contemporaneous most, if not all, interstra titled igneous rocks, ancL 

 most, if not all, fragmentary or agglomeratic igneous rocks. 



