ANNIYEKSAKY ADDEESS OP THE PEESIDENT. 6 1 



reasoning. The agencies producing the change, in all cases where 

 we can ascertain their nature, are heat, water, pressure ; the effects 

 of these acting singly, in pairs, or conjointly can be observed in 

 various cases familiar to every student, and it is possible that the 

 same results may be produced by different amounts of each. As a 

 rule, however, we can distinguish as the results of ^'■contact metamor- 

 phism " the effects which are produced on sediments by the intrusion 

 of igneous rocks ; while the term " regional metamorphism " is applied 

 to the cases where great masses of stratified rocks, buried deep below 

 others, perliaps also subjected to lateral earth-pressures, have been 

 exposed to the action of a moderately and uniformly elevated tempe- 

 rature in the presence of water. To the action of the latter the great 

 masses of schists and gneisses have been by many geologists 

 unhesitatingly referred. They have been regarded as simply the* 

 muds and silts and other sediments, and possibly in some cases the 

 volcanic ejecta, of past geological periods, once more exhumed after 

 a long entombment. Thus at one time many of the crystalline 

 schists and gneisses were unhesitatingly regarded as contemporaneous 

 with strata which, in other localities, teemed with the relics of 

 organisms, and were of Paleozoic or even later age. The last few 

 years have witnessed the growth of a new school in geology. Its 

 members, while admitting the possibility of these identifications, 

 consider that the evidence in their favour has been in so many 

 instances proved to be fallacious, that the onus pi^ohandi lies on 

 him who asserts, not on him who denies the identification. They 

 also are of opinion that the older race of geologists were probably 

 nearer to the truth when they assigned these great masses of apparently 

 stratified crystalline rocks to an age anterior to that of the earliest 

 member of the Palaeozoic period. Thus the crystalline schists and 

 gneisses are now supposed by many experienced geologists to have 

 been produced in those dim ages in this world's history which in- 

 cluded the dawning days of life, and in ages yet earlier than these, 

 when on a recently consolidated crust, and in an atmosphere over- 

 charged with vapour, forces, physical and chemical, were more intense 

 in action than they have ever been since. For this period the names 

 of Pre-Cambrian, Azoic, Eozoic, and Archsean have been proposed*. 

 During the last three or four years, however, the attention of 

 workers has been so forcibly directed to instances of modifications 



* The claim of one or other has been advocated in certain cases with some 

 warmth. Into these contests I do not propose to enter, for I cannot feel 

 much sympathy with them. In a question of this kind it seems to me compa- 

 ratively unimportant what name has the priority of date or who coined it. The 

 main question is, which is most simple and most accurately expresses scientific 

 fact? tfudged by this standard, it appears to me that Azoic and Eozoic are the less 

 desirable, as involving theories, though the latter is probably the more accurate, 

 for it must be remembered that the propriety of the term Eozoic is not in tlie least 

 bound up with the Eozoon controversy. It is in the highest degree improbable 

 that there were no living creatures on the earth anterior to the Cambrian period. 

 So that if life began at any time prior to it, the period in the course of which it 

 began — as we cannot hope to fix the epoch precisely — may fairly be called 

 Eozoic. The other two express a definite fact, the antiquity of the series. Pre 

 Cambrian is the more precise, but I think, on the whole, Archaean preferable. 



