J. W. JUDD ON THE SECONDARY ROCKS OF SCOTLAND. 721 



more littoral conditions in Raasay than in Skye, the sandy mica- 

 ceous shales being less predominant, while coarse sandstones and 

 grits with calcareous concretions full of shells take their place. 



The Lower-Oolite strata appear to occur as far to the northwards 

 as the Shiant Isles ; for in a visit which I paid to that isolated 

 group of rocky islets in company with Dr. Taylor Smith I found masses 

 of greatly altered shale enclosed between gigantic intrusive sheets of 

 coarse dolerite, as described on a previous page (see p. 677). The 

 intense metamorphism to which these shales had evidently been 

 subjected had resulted in converting highly micaceous clays, in 

 places becoming sandy and calcareous, into hard masses like Lydian 

 stone, and in other cases causing them to pass into a remarkable rock 

 with a pseudo-pisolitic structure developed in its midst. For a long- 

 time we searched in vain for any traces of fossils other than those 

 recorded by Macculloch as occurring here, namely the hollow casts 

 of Belemnites ; but at last we were so fortunate as to detect flat- 

 tened impressions of Ammonites, which I was able to identify as 

 Am. Murchisonce, Sow., and Am. corrugatus, Sow. The forms of 

 the Belemnite-casts, too, are in some cases undoubtedly those of 

 Bel. giganteus ; so that I have little hesitation in affirming that in 

 these most remote representatives of the Jurassic system in the 

 Hebrides we have the lowest part of the Inferior-Oolite series. In 

 the district of Strathaird beds of Inferior Oolite occur immediately 

 beneath the great capping of basaltic lava ; but here the amount of 

 alteration which the beds have undergone, owing to their proximity 

 to the axis of the great Skye volcano, is very great indeed, and only 

 at a few points have I been able to detect obscure traces of the 

 characteristic fossils of this horizon. Their relations to the under- 

 lying strata are, however, perfectly clear and unmistakable. 



Still further south, in Ardnamurchan, the Inferior-Oolite strata 

 again make their appearance, and, indeed, occupy a considerable area ; 

 but here, as in Strathaird and the Shiant Isles, they have undergone 

 great alteration. They are frequently, indeed, found to be inter- 

 sected by such a plexus of veins and dykes of igneous rock as to 

 have lost all traces of stratification and every vestige of fossils ; but 

 by tracing these masses over a considerable distance, less altered 

 patches may sometimes be found ; and in such I have detected such 

 characteristic fossils as Ammonites Murchisonce, Sow., Belemnites 

 giganteus, Schloth., Bhynchonella sjpinosa, Schloth., and several other 

 well-known Inferior-Oolite forms. 



Still further south the Inferior-Oolite strata are entirely cut off 

 by the overlap of the Upper Cretaceous. 



The thickness of strata of Inferior-Oolite age exposed in the 

 Shiant Isles does not appear to be very great. There are evidently 

 beds of somewhat different mineral characters exposed there, some 

 being more calcareous, others more argillaceous in composition. Most 

 of the beds were, however, originally clearly arenaceous in charac- 

 ter; but all have undergone great metamorphism through being en- 

 tangled in the great sheets of basaltic rock already described (see 

 section, fig. 6, p. 677). 



3e2 



