Ixxvil PROCEEDINGS OF THE GEOLOGICAL soclETY. [May rgo2. 
all that it implies is that the change in the shape of the rock-mass 
is not due to the formation of visible cracks. 
The microscopic examination of rocks which have been subjected 
to plastic deformation has thrown great light on the nature of the 
process. In some cases, it is due to a re-arrangement of the mineral 
particles, as in certain slates; in others, it is due to fracture and 
trituration of the constituent minerals, as in the rocks for which 
Prof. Lapworth has proposed the term mylonite; and in others it 
is accompanied or followed by recrystallization, as in the typical 
granulites, granulitic gneisses, and phyllites. It is quite possible 
that deformation at ordinary temperatures has never produced holo- 
crystalline schists. 
How far will the ideas to which I have briefly referred furnish us 
with an explanation of the origin of the crystalline schists? Thermo- 
metamorphism will not account for the facts, neither will dynamic 
metamorphism ; but if we combine the two ideas, and recognize the 
fact that thermodynamic metamorphism may be associated with 
the intrusion of molten mineral matter and the formation of mixed 
rocks, we find ourselves in possession of a powerful intellectual 
weapon wherewith to attack many problems connected with this 
puzzling group. 
In saying this, however, | am far from wishing to imply that 
our stock of ideas is sufficient to enable us to deal in a satisfactory 
manner with the rocks in question. It is quite impossible to wander 
over extensive regions composed of crystalline schists, without feeling 
the inadequacy of current theories. Our ideas will change and new 
ideas will arise, but there is every reason to hope that these 
petrographical hieroglyphics, as they have been termed, will 
ultimately be read as easily as we now read the records of the 
stratified rocks. 
My duties as your President are over. I thank the officers, who 
have rendered my task an easy one, and I thank you all for the 
honour which you conferred upon me two years ago, as well as for 
the support which you have accorded to me during my term of 
office. 
