J. W. JUDD ON THE SECONDAKY ROCKS OF SCOTLAND. 707 



in the beds of indurated black rock (resembling Lydian stone) and 

 the crystalline limestone with ophicalcite, into which the shales and 

 limestone are respectively altered. Even here, however, their rela- 

 tion to other rock-masses of known age, and the occurrence of an 

 occasional fossil, enable us to assign the beds in question to their 

 true position in the geological series. 



Prom the above description it will be seen that the Lower Lias 

 of Skye, Eaasay, and Applecross appears to differ from the normal 

 type by the smaller development of the limestone-floors and the 

 prominence of the intervening masses of black micaceous shale. 

 The more northern area of the Lower Lias is cut off by a consider- 

 able interval, in which no traces of the formation are found, from 

 the districts of Ardnamurchan, Morvern, and Mull, in which we find 

 exposures of the Lower Lias assuming characters much more nearly 

 in conformity with those of the typical beds in England. In the 

 southern district of the Western Islands the beds of limestone are 

 much more fully developed than in the northern area ; and the 

 English geologist is everywhere struck by the very close resemblance 

 of the oft-repeated limestone-floors, with only thin shaly partings 

 between them, to the strata of equivalent age in the southern part 

 of this island. 



In the peninsula of Ardnamurchan the Lower-Lias strata are met 

 with at various points, but good exposures of them occur only in 

 the sea-cliffs. On the north side of the peninsula the cliffs at 

 Surdil exhibit great masses of limestone alternating with shale, and 

 crowded with Gryphcea arcuata, Lam., and other fossils. These beds 

 rest on the compact limestones and calcareous grit of the Infralias, 

 which in turn repose on the representative of the Poikilitic. The 

 upper portions of the Lower-Lias strata at Surdil have undergone 

 great metamorphism, being traversed in all directions by innumer- 

 able dykes ; in this part of the series the limestones become highly 

 crystalline, and every trace of fossils is obliterated. 



On the south side of the peninsula of Ardnamurchan the Lower- 

 Lias limestones are well exposed in the reefs below the picturesque 

 ruins of Mingary Castle, and for a considerable distance along the 

 shore between Kilhoan and Sron More. The beds are in places 

 considerably interfered with by masses of basalt, forming both in- 

 trusive sheets and dykes. The lowest beds of the Lower Lias here, 

 which are seen directly reposing on the compact limestones of the 

 Infralias, consist of limestones of somewhat sandy character con- 

 taining numerous specimens of Gryphcea arcuata, Lam., of the typical 

 form. Beds almost made up of the ossicles of Pentacrinus occur here. 



The highest beds of the Lower Lias, which are greatly altered on 

 the north side of the Ardnamurchan peninsula, are, on the south 

 side, admirably exposed ; and the alteration which they have under- 

 gone is small in extent and of merely local character, being con- 

 fined to the immediate proximity of the masses of intrusive rock. 

 We here find, too, clear proofs of the presence of the Subzone of 

 Ammonites semicostatus. It is represented by a thick mass of dark 

 micaceous shale, with only occasional limestone bands, very similar 



