44 
president’s address. 
of Sutherland. The paper on the subject was read in 
December, and will not, I suppose, be published in full till 
May, but abstracts have appeared, and Mr. Teall has very 
kindly shown me sections from the different parts. The 
result may be broadly stated to be the transformation of an 
ordinary plagioclase-augite rock, similar in general character 
to the Eowley stone, with a hornblende-schist scarcely, if at 
all, distinguishable from that of, say, the Lizard district. 
This appears a startling assertion, but the details are so 
worked out that there seems no possibility of doubt on the 
matter. A curious circumstance is that the process has so 
gone on that the parts of the rock which are most nearly 
unaltered have the most altered appearance. There is a good 
deal of alteration in the felspar and augite, and the general 
aspect is rather of that unsatisfactory stage in the history of 
a rock when the constituents have become too full of 
apparently dusty opaque material to be properly transparent 
in thin sections. The next stage shows us hornblende in 
well-developed crystalline masses taking the place of the 
augite which proportionately disappears, and in place of the 
felspar there comes into notice a granular crystalline mass 
which seems to contain both quartz and felspar. Where this 
has gone on to the full extent the original constituents have 
completely disappeared, both as to substance and form, which 
latter in many cases of change remains after the substance 
is completely altered, but the rock is still quite devoid of any 
schistose structure; it might be classed as a diorite containing 
quartz. In certain parts, however, the freshly-arranged mass 
has become involved in some of the great earth movements, 
of which mention has several times been made, which have 
been such potent factors in the formation of the highland 
region, and here the crushing lias resulted in the production 
of the hornblende schist with well-marked layers of horn¬ 
blende in a colourless ground of grains of quartz and felspar. 
Chemical investigation shows that there has been compara¬ 
tively little removed or added, and we seem to have at last 
traced a case of what has often been suspected, what indeed 
has seemed probable, a series of changes not of substance but 
of arrangement; the production of what has always been held 
to be a metamorphic rock, hut out of an igneous not out of an 
ordinary sedimentary one. 
This case shows very conclusively how considerable an 
amount of molecular mobility there is in the silicates in 
presence of water, even at comparatively low temperatures; 
and prepares us for the very low temperature at which it 
seems almost certain that the granites have finished their 
