710 J. W. JUDD ON THE SECONDARY EOCKS OF SCOTLAND. 



landi-he&s here are seen resuming their normal characters. Further 

 east, towards Duart House, they are found to be covered by thick 

 masses of indurated micaceous shales in which fossils are rare. I, 

 however, succeeded in detecting in them several of the forms of 

 Ammonite so characteristic of the Subzone of Ammonites semi- 

 costatus. 



The Lower Lias reappears on the south side of the Island of Mull. 

 At Carsaig the well-marked strata of the Zones of Ammonites semi- 

 costatus and A. Bucklandi are seen cropping out from beneath the 

 Pabba Shales, which are so finely developed at this point. The 

 older set of beds, however, is much disturbed and altered by igneous 

 intrusions ; and as we trace down the series in the direction of 

 Loch Buy, we find the strata completely and somewhat abruptly 

 cut off by the intrusion of volcanic masses of Miocene age. I suc- 

 ceeded in detecting here some of the characteristic Ammonites of 

 both the divisions of the Lower Lias ; and specimens of Ammonites 

 BucMandi, Sow., have been found which attained to a very great 

 size. I received very great assistance during my studies of this 

 part of the Isle of Mull from Mr. A. Maclean, of Carsaig. 



In the precipitous cliffs stretching to the eastward of Loch Buy 

 the Lower-Lias strata are probably represented. But here all the 

 stratified masses are in such close proximity to the great igneous 

 centre of the Mull volcano, and have in consequence undergone such 

 intense metamorphism, that it is almost hopeless to seek to identify 

 the several formations, their fossils having been in almost every 

 instance completely obliterated. 



c. The Middle Lias. 



This division of the geological series is most admirably developed 

 in the Western Highlands. It consists of two well-marked members, 

 which can everywhere throughout the district be fairly well distin- 

 guished, though they are not separated by any sharp line of division, 

 either physical or palseontological. The lower of these members of 

 the Middle Lias consists of sandy shales, and it may be conveniently 

 denominated (after the name of the island in which it is very beau- 

 tifully exposed) " the Pabba Series." The upper member of the 

 Middle Lias, in the Western Highlands, consists of a great thickness 

 of calcareous sandstones, which, from the island in which they are 

 equally well developed, we may call "the Scalpa Series." The 

 palseontological evidence happily leaves us in no doubt as to the 

 geological horizons to which these two series ought severally to be 

 referred ; for each of them contains an abundant and very distinctive 

 fauna. By the study of these faunas it becomes clear that the Pabba 

 Series represents Quenstedt's Lias y, the Zones of Ammonites Jamesoni, 

 A. ibex, and A. Davoi of Dr. Oppel ; while the Scalpa Series is the 

 equivalent of the Lias 5, the Zones of Ammonites margaritatus and 

 A. sjoinatus of the former author. 



The Pabba Shales retain remarkably uniform characters over a 

 wide area, and consist of more or less sandy and very micaceous 



