J. W. JUDD ON THE SECONDARY ROCKS OP SCOTLAND. 711 



shales, with many limestone nodules. At many points, where ex- 

 posed in the cliffs, the beds of this series are apt to be concealed by 

 a talus of fallen blocks, which have descended from the overlying 

 harder beds of the Scalpa Series. But at Hallaig in Baasay in the 

 island of Pabba, and at Tobermory and Carsaig in Mull, there is no 

 difficulty in studying the beds of the Pabba Series and of collecting 

 their fossils, which, at all these localities, are singularly abundant, 

 and sometimes in a fine state of preservation. The greater por- 

 tion of the strata of the Pabba Series must clearly be referred to 

 the Zone of Ammonites Jamesoni, which is perhaps nowhere repre- 

 sented by beds of such great thickness and highly fossiliferons 

 character. At the base are some strata in which Ammonites of the 

 group of the Armati abound ; and these may be regarded as repre- 

 senting the Subzone of Ammonites armatus of Dr. Oppel. In their 

 upper part, and where the sandy shales of the Pabba Series graduate 

 into the calcareous beds of the Scalpa Series, bands of limestone nodules 

 appear in the midst of the shales ; and it is by the gradual increase in 

 frequency of these nodular calcareous bands that the Middle-Lias beds 

 gradually lose their argillaceous character, and pass into calcareo- 

 siliceous rocks. Now a study of the fossils of this intermediate 

 series of beds, which is well seen both in Raasay and Skye, shows 

 that they represent the Zone of Ammonites capricornis of English 

 geologists, and probably the Zones of Ammonites Dav'oi and Am. ibex 

 of Continental authors. 



The masses of calcareous sandstones constituting "the Scalpa 

 Series " are usually highly micaceous, like the Pabba beds below ; in 

 some places they assume ferruginous, and in others argillaceous cha- 

 racters, but generally appear in the form of sandy limestones and 

 calcareous grits of a grey or yellow tint. Their fossils are unmistakably 

 those of the Zones of Am. margaritatus and^4m. spinatus, the two zones 

 being perhaps not very distinctly separated in this district. There 

 is certainly, however, no part of the British Islands where this 

 portion of the Middle-Lias formation is found to be represented by 

 so vast a thickness of strata. Although the mineral characters are 

 tolerably uniform throughout the whole of the Scalpa Series, while 

 many of the species of fossils range from the top to the bottom of 

 it, yet a distinction of the two zones to which its beds belong, can 

 be made out by the prevalence of Ammonites spinatus, Brug., and 

 Oryphcea gigantea, Sow., in its upper beds, and of the varieties of 

 Ammonites margaritatus, de Montf., with OrypTicea cymbium, Lam., 

 in the lower beds. Near the Sound of Scalpa, and in Strathaird, the 

 Middle-Lias strata, though clearly recognizable by their position, 

 have, in consequence of their proximity to the great volcanic centre 

 of Skye, undergone such changes that many of their mineral cha- 

 racters have disappeared, and almost all traces of their fossils have 

 been obliterated. Intersected as they are by multitudinous dykes, 

 and changed for the most part into brittle quartzites and burnt 

 shales resembling Lydian stone, it is only here and there that one 

 is fortunate enough to detect the cast or impression of a fossil upon 

 which to base an opinion concerning the age of the strata which 



