ANNIVERSAET ADDRESS OF THE PRESIDENT. Ill 



which has prevailed since life has left its trace on the pages of the 

 great Stone Book of iSTature. 



Various attempts have been made to describe the genesis of the 

 earlier Archaean rocks, but at present, as it appears to me, we can do 

 little more than vaguely conjecture. On the one hand, it seems 

 clear that many gneisses are formed after compression from granites, 

 many hornblende-schists from dolerites, and possibly some other schists 

 may be the result of mineral change in igneous rocks of suitable 

 constitution. At the same time, as I have shown, some even among 

 the oldest gneisses exhibit structures which appear to distinguish 

 them from granites, and the presence of limestones suggests at any 

 rate some kind of stratification or stratified precipitation. The 

 indications of sedimentation become more clear as we ascend in 

 the series, so that we cannot avoid assigning a sedimentary origin 

 to many of the bedded gneisses, schists, limestones, quartzitcs, &c. 

 Some have suggested that among these oldest gneisses we have 

 ]-epresentatives of the earliest crust of the globe, though modified by 

 subsequent mineral change, and that we may see in them the roots 

 of primaeval volcanoes and metamorphosed remnants of their associ- 

 ated beds of ashes. This may well be, for we should expect that 

 for a time, after the first solidification of the globe, volcanic action 

 (as in the phase of history stereotyped by the moon) would be more 

 universal and on a grander scale than it has ever been since. But, 

 unfortunately, we have little to guide us as to the nature of the 

 structures which would be assumed by volcanic materials under 

 circumstances such as these. 



A very learned and ingenious attempt has recently been made by 

 Dr. Sterry Hunt to explain the origin of the crystalline rocks. By 

 his hypothesis, termed the Cre7ietic, the primary crust of the globe, 

 last solidified by cooling from a state of igneous fluidity, is supposed 

 to have been a basic quartzless rock. This is conceived to have been 

 fissured and rendered porous during crystallization and refrigeration, 

 so as to have become permeable to considerable depths to the waters 

 subsequently precijDitated upon it. By their action, the crystalline 

 stratiform rocks (the fundamental granites and the granitoid gneisses) 

 were derived from it. Subsequent disturbances would corrugate 

 and elevate these, giving rise to fissures from which the underlying 

 basic stratum would be erupted, and from the subaerial decay of 

 the two types new factors would be introduced into the rock-forming 

 processes, and the more variable later gneisses and schists produced. 

 This hypothesis, no doubt, accounts for many facts, and is a suggestive 

 and valuable contribution to the solution of a complicated problem. 

 At the same time, I must remark that the author regards the subject 

 too exclusively from the point of view of a chemist, and takes more 

 for granted than appears to me warranted by the facts of Nature, 

 as learnt in the field, or from study of rock- structures under the 

 microscope ; bat while I think some of the petrologioal statements 

 dubious, some of the proposed stratigraphical orders improbable, and 

 some of the generalizations too sweeping, I must say that the 

 tendency of the evidence which he has brought together so labori- 



