132 J. W. JUDD ON THE STRUCTURE AND 



Seat were produced by tivo entirely distinct series of volcanic outbursts 

 upon the same site, the interval between which was marked by the 

 deposition, the subsequent upheaval, and the removal by denudation 

 of at least 3000 feet of Carboniferous strata. 



That the earliest of these periods of volcanic eruption was con- 

 temporaneous with the deposition of the lower portion of that 

 formation to which he gave the name of " the Calciferous Sandstone" 

 — a term now very generally adopted by geologists — was clearly 

 perceived by Maclaren. He did not, however, succeed in obtaining 

 any data for fixing the age of the supposed later series of volcanic 

 outbursts. 



In 1854, Edward Forbes, coming to Edinburgh fresh from the 

 study of those lavas in the Western Isles which the researches of 

 the I)uke of Argyll and himself had proved to be of Tertiary date, 

 originated, though he did not publish, the suggestion that the sup- 

 posed newer volcanic eruptions of Arthur's Seat might also have 

 taken place during the same epoch. 



In preparing the one-inch map of the district with the accom- 

 panying memoir of the Geological Survey, Prof. Geikie, who has 

 given so much attention to the geology of the district, adopted in 

 1861 this opinion of the Tertiary age of the rocks in question as the 

 probable one * ; at a later date the Secondary age of these rocks was 

 suggested by the same author f ; but in 1 867 both of these views 

 were abandoned in favour of the opinion that they are of Permian 

 date %. 



While studying, during several years past, the volcanic rocks of 

 Edinburgh, in connexion with those of other parts of Britain, I 

 have been gradually led to the conclusion that the supposed second 

 series of volcanic outbursts at Arthur's Seat — the suggestion of even 

 a probable date for which has proved so perplexing a problem for 

 geologists — really had no existence ; but that, on the contrary, all 

 the phenomena of the district are capable of being explained on the 

 hypothesis of a single and almost continuous series of eruptions, 

 confined to one geological period — the Lower Carboniferous. 



I must here pause, however, to perform an act of justice to the 

 memory of Maclaren. During his later years he had continued his 

 patient researches among the rocks of Edinburgh, visiting, for the 

 purpose of comparison, some of the chief volcanic districts of Europe. 

 The object which he seems to have kept before him was a recast of 

 his original work. But, unfortunately, the preparation of this 

 important task was too long deferred by the talented but cautious 

 author; and although, shortly after his death at the advanced age 

 of 85, a new edition of the work was published, yet it proved to 



* Sheet 32 of the 1-inch Map of the Geological Survey of Scotland, and 

 Memoir on the Geology of the Neighbourhood of Edinburgh, &c. 



t Sheet 2 of the 6-inch Map of Edinburghshire, of the Geological Survey of 

 Scotland (1864). See also the Map accompanying ' The Scenery of Scotland 

 viewed in connexion with its Physical Geology' (1865). 



\ See ' Brit. Assoc. Eep.' for 1867 (Dundee Meeting), Trans, of Sect. p. 51, 

 and. subsequent publications. 



