1873.] 



JUDD THE SECONDARY ROCKS OF SCOTLAND. 



179 



large size, abound, as in the Clynlish stone ; but it is composed of much 

 coarser materials than that rock. Slabs also occur, traversed by 

 ripple-markings and worm-tracks, or covered with casts of vegetable 

 fragments and small shells. The strata sometimes greatly resemble 

 the Collyweston, Stonesfield, and similar " slates " of England, and 

 present clear indications of having been deposited under very shal- 

 low-water conditions. 



These marine beds are best seen at Allt-na-cuil, where, both above 

 and below the waterfall, there are quarries in this rock. They are 

 also seen on the other side of the anticlinal referred to, where a cutting 

 has been made on the Sutherland Railway. This rock forms a 

 valuable building-stone for certain purposes. It is very soft when 

 first quarried, hardens rapidly on exposure, and is very durable. 

 Although of so much coarser texture, it appears, in its power of 

 resisting weathering action, to greatly resemble the celebrated 

 " Roach-bed" of Portland, and, like it, is used for the copings of walls 

 and similar situations. 



The fauna of these beds shows that they belong unquestionably to 

 the Upper Oolites, and is as follows : — 



Fossils of the Marine Sandstones of Allt-na-cuil fyc. 

 (IJpper Oolites). 



Belemnites obeliscus, ? Phil. 

 Ammonites Eudoxus, 1)' Orb. 



biplex, Sow, ? var. 



Achilles, De Loriol (non If Orb.). 



triplicatus, Sow. 



• mutabilis, Sow. 



Natica, sp. 



Area, sp. 



Avicula expansa, Phil., var. 



Perna subplana, Etallon. 



Ptei'operna, sp. 



Peeten demissus, Phil. 



articulatus, Schloth. 



, sp. 



Hinnites inaequistriatus, D' Orb. 

 Ostrea Rcemeri, Quenst. 



expansa, Sow. 



deltoidea, Sow. 



Ebynchonella pinguis?, Bom. (very- 

 abundant). 



pectunculoides ?, Etallon. 



Serpula, sp. 

 Cidaris, sp. (spines). 



' S P- . 



Acrosalenia, sp. (spines). 



Equisetites, sp. 



Wood (abundant). 



Fucoid markings? 



These marine beds are overlain by a considerable thickness of 

 strata, of estuarine origin, which are exhibited in the neighbourhood 

 of Allt-Chollie (Colyburn), where, however, they are somewhat 

 obscure, owing to the greatly contorted and crushed condition of the 

 beds, which has been already described (page 118, fig. 3). On the 

 opposite side of the anticlinal, however, between Allt-na-cuil and 

 Lothbcg Point, they are much more favourably exposed for study. 

 They are of very considerable thickness, several hundred feet at 

 least, and consist of alternations of white sandstones, containing only 

 a few plant-remains, and beds of very finely laminated, black, car- 

 bonaceous, sandy shales. In the lower part of the series the white 

 sandstones predominate ; but as we pass upwards the laminated argil- 

 laceous beds become of greater thickness, and at last form the prin- 

 cipal part of the mass. In the highest beds, of which admirable 

 sections are exposed at the artificial opening through which the 



N 2 



