ANNIVERSAEr ADDEESS OF THE PRESIDENT. II3 



non-Archaean age of the deposit is known, we find that the results of 

 metamorphism are comparatively slight, and that the schistose rock 

 thus produced is very far removed from a true schist. Further, 

 when these are underlain by gneisses and crystalline schists, as in 

 the Alps, there is not a gradual transition into the latter, but an 

 abrupt change. Now if a gradual transition could only be found as 

 we passed downwards from the lowest Palaeozoic rocks through 

 the upper part of the Archaean series, instances of this (as repre- 

 senting one period only of the earth's history, and one of which the 

 rocks were less resistant than their highly crystalline predecessors) 

 would naturally be rarer. 



The Correlation of Arclicean Rocks. 



Let us now see what lithological parallels suggest themselves 

 between the rocks of the regions noticed in this address. In doing 

 this we must as far as possible make allowance for the results of 

 subsequent compression and crushing, and found our comparisons 

 either upon uninjured specimens which may sometimes be found, or 

 those in which what we may term " a restoration " is not difficult to 

 the practised eye. We may also, if due caution be exercised, use 

 for comparison rocks which, after similar treatment, present marked 

 lithological identities. 



There is a very close resemblance between the Laurentian gneiss 

 of Canada and the Hebridean of Scotland (in which may be included 

 certain rocks of the Central Highlands *). In many cases I could 

 only distinguish a Canadian from a Scotch specimen by its label, 

 llany similarities to these may be noted in the coarse gneissic and 

 granitoid rocks of Anglesey, and with them we may venture to com- 

 pare the granitoid rocks near Caernarvon. Some of the gneisses of 

 the Malvern Hills and the Wrekin district seem to me onlj to exhibit 

 varietal differences ; and those which I have described as occurring in 

 the lowest part of the Alpine series (1) and (2), notwithstanding 

 differences in colour and more indications of an igneous origin, appear 

 to me generally identical. The coarse gneisses of the Schwartz- 

 wald and Odenwald, and other districts in Central Germany, have also 

 a Laurentian facies, which, however, is generally admitted. 



The resemblance between the Lepontine gneisses (3) and Casanna 

 series (4) of the Alps and the Montalban series of America is very 

 striking ; and to these we often find close parallels in the more 

 micaceous gneisses and mica-schists, often rich in garnets, of the 

 Highlands. I have seen specimens of so-called Hurouian of similar 

 types. It is possible that some of the so-called gneisses (fine- 

 grained) of Anglesey may bo correlated here ; but my specimens (in- 

 cluding some of the rock claimed as halleflinta) would be more 

 properly designated quartzose mica-schist, and in general structure 

 remind me of Alpine rocks that lie at a slightly higher horizon. It 

 is very probable that some of the quartzose schists abundant in the 

 Central Highlands (e.cj. on the Highland Eailway above Blair Athol 



* E. g. from near Loch Shiel, as described by Dr. Hicks, whom I have to 

 thank for specimens (see Q. J. G. S. vol. xxxix. p. lo5). 



