J. W. JUDD ON THE SECONDARY ROCKS OF SCOTLAND. 679 



their fossils have been often to a great extent and sometimes com- 

 pletely obliterated. It is, indeed, only at considerable distances from 

 the centres of igneous activity that the geologist has the smallest 

 chance of finding these sedimentary masses in a sufficiently unaltered 

 condition to supply him with useful records of the periods during 

 which they were deposited ; and even in some cases where they are 

 at a sufficient distance from the great volcanic centres to have 

 escaped in the first instance from metamorphic action, subsequent 

 smaller outbursts, which have taken place in close proximity to them, 

 may have produced injurious effects on their fossil contents, as is well 

 seen beneath Beinn Shiant. 



Among the difficulties caused by the complication of stratified 

 deposits with intrusive sheets we may mention that of determining 

 their exact thickness, the task being in some cases, indeed, as in the 

 north of Eigg and in Trotternish, rendered absolutely hopeless in 

 consequence of the number and capricious behaviour of the intrusive 

 masses lying in their midst. 



Of the wonderful changes at times effected in the character of the 

 sedimentary strata, of the complex intervening of bedded and intru- 

 sive masses, such as is seen in Strathaird, Ardnamurchan, Rum, and 

 Mull — where the bulk of the intrusive sheets and dykes taken collec- 

 tively sometimes far exceeds that of the older stratified masses among 

 which they have been forced — it is impossible to convey any adequate 

 idea to those who have not had an opportunity of visiting the district. 

 Macculloch's drawings of the dykes of Strathaird* and of the won- 

 derful section of Stronbeg in Ardnamurchanf may perhaps give some 

 faint idea of the strangeness, complexity, and interest of the pheno- 

 mena in question. 



But in spite of the numerous difficulties, the serious obstacles, 

 and the trying disappointments which the investigator of the Secon- 

 dary strata of the Western Isles must be prepared to encounter 

 in his task of detecting and studying these isolated patches of fos- 

 siliferous rock, of reasoning concerning their relations, and of 

 combining these scattered relics of a long series of epochs in the 

 world's past history, he finds most ample compensation in the 

 absorbing interest of the subject ; nor will he begrudge any 

 labour or pains when he reflects upon the importance of these sin- 

 gularly preserved fragments of geological evidence in enabling 

 us to reconstruct the physical features of this portion of the globe 

 during long past periods, and to unravel the complicated series of 

 changes which the district now forming the Highlands of Scot- 

 land has undergone in the past. I cannot, indeed, conceive of a 

 work more delightful to any one who has felt the least touch of the 

 enthusiasm of research than that of seeking for and piecing toge- 

 ther these torn, blotted, and almost utterly defaced pages of the 

 geological record, and weaving from them a connected story. 



* 'Western Isles of Scotland.' Atlas, pi. xiv. fig. 5, and pi. xvi. fig. 1. 

 t Ibid. pi. xxxiii. fig. 1. 



