ANNIVERSARY ADDRESS OF THE PRESIDENT. xHx 



expensive for the practical purposes of the geologist. I am able to 

 state, that the maps are now being engraved on the smaller scale, 

 and that a commencement has already been made in the use of them. 

 Mr. Jukes announced to the Geological Section at Liverpool that the 

 northern part of the county of Wicklow was already completed and 

 coloured geologically. 



The last Number of the Memoirs of the Geological Survey (De- 

 cade III.) is devoted to the figures and descriptions of Trilobites, 

 which, as our late President observes in the Introduction, are remark- 

 ably characteristic of well-defined geological horizons. The study of 

 these forms is consequently of great importance to the geologist 

 whose labours are directed to the investigation of the more ancient 

 rocks, to which they exclusively belong. The figures and descriptions 

 in this Decade are by Mr. Salter. 



The question of the cleavage and foliation of the older crystalline 

 rocks is one which has on several occasions occupied our attention at 

 the evening meetings, and has given rise to many interesting discus- 

 sions. To judge from the various opinions entertained on this sub- 

 ject, the question still requires much careful examination, not only in 

 a theoretical point of view as to the causes which may have produced 

 these effects, but even as to the facts themselves on which these 

 theories are to be founded. It would therefore be premature to 

 enter fully into this question, but I will endeavour briefly to lay 

 before you the evidence which has been brought forward, and the 

 different views entertained upon the subject. Three papers have 

 been lately read before the Society, describing the various phseno- 

 mena observed by the different authors ; the first was a paper by 

 Mr. Sharpe, '* On the Structure of the Crystalline Rocks in the 

 neighbourhood of Mont Blanc ;" the second was by Mr. Evan Hop- 

 kins, *' On the Laminated Structure of the Primary Rocks ;" and the 

 third was read at our last meeting by Mr. David Forbes, " On the 

 Foliated Rocks of Norway." 



The universality of the views entertained by Mr. Evan Hopkins, 

 and the fact of his having already, in 1850, stated them partially to 

 the Society, induce me to notice them first. On the former occa- 

 sion, in his paper on the " Structure of the Crystalline Rocks of the 

 Andes, and their Cleavage Planes," Mr. Hopkins endeavoured to 

 show that in a section of many hundred miles, the crystalline rocks 

 of South America were universally characterized by vertical or almost 

 vertical lines of cleavage, and that these cleavage planes had a uni- 

 form meridional direction or strike, thereby separating innumerable 

 varieties of granites, gneiss, schists, hornblende, chloritic slates, 

 porphyries, &c., into great meridional bands. In his paper of this 

 session, Mr. Evan Hopkins has endeavoured to show, that in all 

 countries, in all regions, in all quarters of the globe, the old crystal- 

 line rocks have a vertical cleavage, with a north and south direction. 

 This view he lays down with absolute universality, illustrating it by 

 sections of many thousand miles made by himself in various parts of 

 the world. Mr. Hopkins subsequently admitted exceptional cases, 

 but maintained the generality of his law, stating that when these 



