185/.] WRIGHT LIAS FOSSILS FROM SKYE. 35 



with a fine muddy matrix, it is difficult to count the numbers accu- 

 rately. The septa are of unequal length, and they are thin, waved, 

 and granulated on their upper surface ; the columella is absent or 

 rudimentary, and the point of convergence at the bottom of the 

 calyx is always excentral. 



Dimensions. — Longest diameter of calyx y%ths of an inch ; trans- 

 verse diameter y<jths of an inch ; depth of the calyx -^-ths of an inch. 



These corals were noticed by Sir Roderick Murchison* as Poly- 

 pifers of the genus Astrcea, and compared to the coralline bodies 

 found in the Lias at Ledbury near Bridgewater. The coral-bed was 

 found by Mr. Geikie at Lussay underlying calcareous grit and sand- 

 stone of the Lower Lias ; it was irregularly about 3 feet thick, and 

 the corals are enveloped in a fine dark mudstone : the coral-bed rests 

 on a thin band of hard blue limestone, beneath which is a stratum of 

 greenish micaceous nodular sandstone containing Cardinia concinna, 

 Agassiz. 



Isastrcea Murchisoni closely resembles another species of the 

 same genus found in the Lower Lias near Evesham, Warwickshire, 

 Is. Haimeii, Wright ; but it is distinguished from that species by 

 having the calices larger, the mural edge narrower, the septa thinner 

 and more waved ; the columella more excentral. The two corals 

 require a careful comparison to detect their diagnostic characters. 

 I dedicate this species to Sir Roderick Murchison, to whose re- 

 searches we are indebted for much valuable information on the geo- 

 logy of the Hebrides. 



Having thus critically examined each of the species contained in 

 this collection of Lias fossils from the Isle of Skye, the following 

 conclusions may be inferred from their study : — 



1st. That the Lower Lias is represented at Lussay by greenish 

 micaceous sandstone, overlaid by hard blue limestone, on which rests 

 a bed of corals {Isastrcea Murchisoni, Wr.) wrapped in a dark mud- 

 stone, the coral very closely resembling a species found in the Lower 

 Lias of Warwickshire ; the coral-bed, 3 feet in thickness, is over- 

 laid by calcareous sandstone and compact blue limestones. Un- 

 fortunately no Ammonite has been found in these beds, so that 

 their precise age cannot be determined ; still, however, the presence 

 of Cardinia concinna, Zieten, is, per se, good evidence that the 

 greenish micaceous sandstones with Cardinice belong to the Lower 

 Lias ; for that shell is found only in the lower beds in France and 

 Germany, its true position in Wurtemberg having been ascertained 

 to be below the Bucklandi-bed, where it is associated with Ammo- 

 nites angulatus, Schloth. 



2nd. The " Pabba-shales " belong unquestionably to the Middle 

 Lias, as defined in the beginning of this paper ; they appertain to 

 their lower division, which includes the Jamesoni-bed, the Ibex-bed, 

 and Davcei-bed ; a comparison of the species collected by Mr. Geikie 

 with the list of the Middle Lias species inserted at pages 24 & 26 is 

 conclusive as to the age of the Pabba-shales. The number of leading 



* Trans, of the Geol. Soc. 2nd series, vol. ii. p. 368. 



d 2 



