J. W. JUDD ON THE SECONDARY ROCKS OF SCOTLAND. 727 



developed, nor do they at any point in the area exhibit clear or 

 continuous sections. They appear to consist of dark blue shales, 

 perfectly similar in character to the Oxford Clay of England, and 

 containing septarian nodules, masses of pyrites, and occasionally 

 much wood in. the form of jet. At some localities they include 

 irregular bands of argillaceous limestone. 



Although so imperfectly exposed, it is clear, from the nature and 

 position of the fragments of the formation which are seen, that beds 

 of this age must underlie great tracts of the Miocene basalts of the 

 Hebrides. The strata, too, are not improbably of very considerable 

 thickness, although the slipping of the basaltic masses over them 

 wherever they make their appearance prevents us from making any 

 approach to an estimate of that thickness. 



It is, indeed, to this slipping of the great masses of columnar and 

 massive lava rocks upon the insecure foundation of the Oxford Clay 

 that the striking scenery of the eastern side of the Trotternish 

 peninsula, so well exemplified by the Quiraing and the Storr rocks, 

 owes its origin. Here the Oxford Clay appears at great elevations, 

 its fossils being collected occasionally during drainage -operations ; 

 while westward it dips away like the underlying estuarine beds, and 

 disappears beneath the sea-level. Traces of it, however, are found at 

 Duntulm, Mugstock, Uig, and some other points. 



In Eigg, at Laig Bay, the same beds, with precisely similar cha- 

 racters and fossils, occur, but are only exposed at a few points along 

 the shore at low water ; they can only be satisfactorily examined during 

 spring-tides. Possibly, although concealed by shingle and vegeta- 

 tion, a trace of the same set of strata occurs in the neighbouring 

 island of Muck. To the southward, however, no traces of the for- 

 mation have been detected. 



Although the Oxford-Clay strata of the Western Highlands are 

 so strikingly similar in character to those of England, the beds on 

 which they repose are, as we have seen, of entirely different character. 

 With respect to the question of the strata which may have been 

 deposited above these Oxfordian rocks of the Hebrides, I will only 

 refer to what I have already said as to the unreliability of the nega- 

 tive evidence in this case, and to the possibility, if not the proba- 

 bility, of rocks of Upper-Oolite and Neocomian age having originally 

 existed in the Western as well as in the Eastern Highlands. 



The Oxford Clay of both Scotland and England must have been 

 deposited in a sea of considerable depth ; and it is probable that its 

 beds originally extended over a great part, at least, of what is now 

 the area of the British Islands. Indeed, so strikingly similar is the 

 formation in its mineral characters and the succession of its forms of 

 life over the greater portion of the Anglo-Germanic area, that there 

 can be no doubt as to the Oxfordian sea of that life-province being of 

 very wide extent, as well as of considerable depth, and not broken 

 up into a number of isolated portions. We find, however, in York- 

 shire and elsewhere, indications of the prevalence of more littoral 

 conditions, proving probably that some islands rose above the surface 

 of this great Oxfordian sea. The position and relations of these, so 



