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



The Upper-Lias formation in the Western Highlands remarkably 

 resembles both in the character and succession of its beds and its 

 fossil remains the equivalent strata in England. In both districts 

 we find the formation made up of laminated blue clays, contain- 

 ing argillaceous nodules, with much pyrites and jet in certain of 

 its beds. This parallelism of the Scottish Upper Lias with that of 

 England comes out in an even more striking manner when we study 

 the distribution of organic remains in their several members. Thus, 

 in the upper part of both we find an abundance of Ammonites com- 

 munis, Sow., and similar forms, associated with Posidonomya Bronni, 

 Voltz, and Belemnites, while at the base strata characterized by the 

 abundance of Ammonites serpentinus, Rein., Am. radians, Rein., 

 Am. elegans, Sow., and many other species of the group of the 

 Falciferi, are equally distinctive of the beds. 



The thickness of the Upper-Lias series in the Western Highlands is 

 not very great. It averages perhaps from 75 to 80 feet, and occasion- 

 ally, but rarely, reaches 100 feet. On the other hand, it is sometimes 

 perhaps as little as 60 feet thick. Mr. Tate gives a measured sec- 

 tion taken on the east side of Portree Harbour, which shows the Upper 

 Lias as only 15 feet 7 inches thick ; but as the section here is 

 rendered somewhat difficult of interpretation through the numerous 

 slipped masses, I have little doubt that the beds enumerated do not 

 comprise the whole thickness of the formation at this point. 



To Dr. Bryce and Professor Tate we are, as already mentioned, 

 indebted for first pointing out the existence of the Upper Lias in 

 Skye ; but it seems to me, from a reexamination of their sections, that 

 they have almost everywhere underestimated its thickness, having 

 been betrayed into this mistake by the slipped condition of the beds 

 in the great mural precipices and the interruption and confusion 

 produced in the beds by the intrusive sheets of dolerite which are 

 so numerous at the localities where the formation is exposed. 



In Raasay the same strata are present, as I have been able to 

 satisfy myself on several different occasions. Though certainly from 

 80 to 100 feet in thickness, they nowhere exhibit good sections, 

 being almost always buried under talus from the beds above and also 

 grass-covered. 



Between Leac and Eearns, however, above the great development 

 of the Scalpa Series, they consist of black laminated highly micaceous 

 and ferruginous shales with Belemnites Voltzii, many Ammonites of 

 the group of the Falciferi, such as A. serjpentinus, Rein., A. fahifer, 

 Sow., and A. radians, Rein., but all small and crushed, and some other 

 shells. The same beds make their appeance, but even more obscurely, 

 further to the north, in the precipices of Screpidale. 



The Upper-Lias strata are certainly present in the district of 

 Strath in Skye, and most probably also in Ardnamurchan ; but 

 in both these areas the beds are so greatly metamorphosed as to be 

 only recognizable by their relations to the Middle Lias and Inferior 

 Oolite respectively. In Mull they have nowhere been detected, the 

 older strata being everywhere overlapped by the Cretaceous rocks. 



