J. W. JUDD ON THE SECONDARY ROCKS OF SCOTLAND. 697 



fossils ; but such is the hardness and intractability of the matrix in 

 which they are enclosed, that it is seldom possible to disengage them 

 in any thing like a satisfactory condition. Certain beds crowded 

 with specimens of Ostrea irregularis, Miinst., occur in the series, and 

 others almost wholly made up of corals ; and these latter beds abound 

 with species of Gasteropoda, few of which, however, can be obtained 

 in a sufficiently perfect condition for specific determination. 



The limestones above described alternate with beds of sandstone 

 and calcareous grit, which often contain numerous pebbles of quartz, 

 and occasionally pass into conglomerates. At Applecross, where 

 they can be very conveniently studied, these arenaceous strata inter- 

 calated in the Infralias are clearly of estuarine origin, and contain 

 thin and imperfect seams of coal ; but in Skye, Ardnamurchan, and 

 Mull the sandy strata of the Infralias, though clearly of littoral 

 origin, appear to contain marine fossils throughout. 



There seems to be no room for doubt that the Infralias strata of 

 the Western Isles are perfectly conformable with the subjacent 

 Poikilitic, into which in some cases they appear to graduate down- 

 wards insensibly. The locality in which the details of the series of 

 strata can be best studied is that of Applecross ; but here the thick- 

 ness of the series cannot be determined ; on the shore of Eaasay, 

 opposite to Applecross, this thickness can be estimated, though 

 the details cannot be well made out. The result of a careful 

 examination of the question shows that the thickness of the Infra- 

 lias in Eaasay and Applecross cannot be less than from 150 to 200 

 feet; while in Strath in Skye, as seen between Lussay and Obe 

 Breakish, the formation has at least an equal development. In the 

 interior of the island of Skye, about Kilbride and Loch Slapin, the 

 Infralias limestones, repeated by faults, are found to be greatly 

 altered in consequence of the proximity of the great intrusive masses, 

 and pass into fine saccharine marble and ophicalcite, as described 

 by Dr. Macculloch and Prof. Geikie. The sandstones which alternate 

 with the limestones are changed into quartzite. 



The Infralias, when traced southwards from Applecross, Eaasay, 

 and Skye, is found gradually to lose its importance, and to become 

 diminished in thickness. While in Ardnamurchan the strata in 

 question are moderately well developed, in Morvern and Mull they 

 are seen to be reduced to a comparatively rudimentary condition. 

 Possibly in the extreme south of the island of Mull they regain 

 something of their former thickness ; but, unfortunately, the rocks 

 are here so greatly altered, and their fossils so completely oblite- 

 rated through their proximity to igneous intrusions, that it is im- 

 possible to arrive at any certain conclusion as to where one formation 

 ends and another begins. 



It is worthy of remark that in the Infralias of the west coast of 

 Scotland the " Zone of Avieula contorta " does not appear to be 

 distinctly developed. 



The section of the Infralias strata at Applecross is probably with- 

 out its equal in the "British islands, whether we regard the thickness 

 of the strata representing the period, or the variety and beauty of 



