1889.] on the Highlands of Scotland and the West of Ireland. 635 



doubtful impressions and the casts of worms. The fossiliferous bands 

 are to be more thoroughly searched this summer, and it is hoped that 

 something more determinable may be obtained from them. 



Nevertheless, indistinct though these relics undoubtedly are, they 

 may claim the interest which arises from their being at present the 

 very oldest traces of organised existence yet found within our islands. 

 Murchison classed the red sandstones of western Sutherland and Eoss 

 as " Cambrian," inasmuch as he found them to underlie unconformably 

 strata containing what he believed to be Lower Silurian fossils. It 

 is not improbable, however, that they belong to an older time than 

 any of the Cambrian rocks of "Wales. 



That the red sandstones of the north-west of Scotland were laid 

 down in shallow water seems to be clearly indicated by their current- 

 bedding and ripple-marks, as well as by the occurrence of bands of 

 conglomerate among them on many successive horizons. Yet they 

 retain these characters throughout a depth of some 10,000 feet. We 

 can walk over their edges and count every successive stratum for a 

 thickness of more than 300U feet along the sides of a single mountain. 

 How, then, could such a continuous mass of shallow-water deposits 

 be accumulated? I am not sure that any wholly satisfactory answer 

 can be given to this question, which is one that arises in the investi- 

 gation of various epochs of geological history. That the basins must 

 have been due to local subsidence can hardly be doubted. We may 

 suppose that this downward movement continued at the same 

 time that the ridges which bounded the hollows continued to be 

 forced upward. New shore-lines would thus be brought to the level 

 of the water, and coarse shingle might be swept down upon pre- 

 viously dej)0sited fine sediment. If occasionally the barrier between 

 the basins and the open sea were partially submerged, the muddy 

 ferruginous water of the enclosed tracts might be cleared out and the 

 denizens of the sea might for a time enter them. Possibly the grey 

 and dark shales may mark these irrujDtions of the ocean. 



That similar conditions of geography prevailed at that period in 

 the extreme north-west of Europe is indicated by the fact that in 

 Norway a group of red sandstones and conglomerates known as the 

 " Sparagmite rocks " is interposed between the Archaean gneiss and 

 the oldest of the fossiliferous formations. In these Scandinavian 

 rocks we probably see traces of the extension of similar enclosed 

 water-basins along the eastern border of the primeval Atlantic Ocean 

 northwards among the hollows of the Archaean land. 



Before the next great geological period these basins had been 

 entirely eflaced, and the geography of the region had wholly changed. 

 This transformation is probably traceable to two causes. First, the 

 terrestrial movements which led to the formation and continuance of 

 the basins may in the end have caused their extinction by raising 

 them into land, and possibly at the same time by folding and Assuring 

 their accumulated deposits. Secondly, as soon as these deposits, 

 whether split open or not, were exposed to the atmosphere they would 



