age of Arthur's seat, Edinburgh. 133 



be little more than a reprint of the former one. A few notes and 

 additions nevertheless serve to indicate some of the modifications 

 or developments of the author's opinions. 



It was after I had arrived at the conclusion already enunciated, 

 that only one series of volcanic eruptions had taken place at Arthur's 

 Seat, that I found in the second edition of ' The Geology of Fife and 

 the Lothians,' page 47, the proof that Maclaren had himself aban- 

 doned his original views upon the subject. After the passage from 

 his former edition on the second series of eruptions, he adds in 1866, 

 " Such was my opinion in 1839. I am now satisfied that the trap- 

 tuff constitutes only one deposit, and that the second period of 

 eruption after so long an interval had no existence." 



It will not be necessary to apologize to this Society for bringing 

 before it new observations, and deductions from them, on a district 

 so intimately associated with some of the most important movements 

 in the history of our science as Arthur's Seat. And if I may be 

 permitted to be the interpreter of the latest and posthumous ideas 

 of one to whose writings I am so much indebted for instruction as 

 Charles Maclaren, it will be to me a source of no small gratification 

 and pride. 



In seeking to explain the structure of Arthur's Seat, there are 

 three classes of objects which the geologist may with advantage 

 appeal to for purposes of comparison and illustration. These are 

 as follows : — 



I. The numerous volcanic vents in a similarly ruined condition 

 to Arthur's Seat, which are found scattered all over the districts of 

 Forfar, Fife, and the Lothians. Nowhere, perhaps, can the pheno- 

 mena connected with these old centres of eruption during the Car- 

 boniferous period be so admirably studied, in association with one 

 another, as in the group of hills overlooking Edinburgh ; but, never- 

 theless, many of the neighbouring vents will be found by the geologist 

 to illustrate in an especially clear manner some particular point of 

 their common structure. 



II. The Tertiary volcanoes of the Hebrides, which, as I have 

 recently pointed out to this Society, are so admirably dissected by 

 denudation, furnish us with a kind of middle term between the 

 fossil volcanoes of Central Scotland and those which we still see in 

 a state of activity. Viewed in this light, as affording a link by 

 means of which we may more easily compare a series of volcanic 

 skeletons with another of perfect volcanoes, such small denuded cones 

 as Beinn Shiant in Ardnamurchan are of especial interest. 



III. In many districts where active or but recently extinct vol- 

 canoes abound, we cannot fail to recognize, in spite of their different 

 states of preservation, numerous counterparts of structure, similarities 

 of relation, and identity of materials with the old Carboniferous 

 volcanic tracts of Central Scotland. 



In approaching the study of this question it will be well, in the 

 first place, to eliminate all those portions of the subject concerning 

 the interpretation of which no difficulties now any longer exist. 

 Fortunately, these are by no means inconsiderable ; for concerning 



l2 



