50 



in the upper part of the hed. The limestone, shale, and coal seams 

 extend under high-water mark, and when the tide is very low con- 

 siderable pieces of coal are often dug out from beneath the sand 

 and mud covering the tide-way. Several sinkings have been made 

 here for the purpose of discovering workable coal seams, but without 

 success. The fossils by which the strata were identified as belonging 

 to the carboniferous system are given in the following list. The 

 species have been determined by Mr. Frazer, from specimens in his 

 collection and our own : 



Plantae. 

 Sphenopteris bifida, not uncommon in the shales. 



affinis, ditto, 



furcata, ditto, 



dilatata (rare). 



Pecopteris nervosa (rare). 



Calamites nodosus, abundant in the sandstone and shale, 



undulatus. ditto. 



Trigonocarpmn olivaeforme (rare). 



Brachiopoda. 



Producta punctata, not abundant. 



sulcata, ditto. 



Spirifer semicircularis, somewhat common. 



trigonalis (rare). 



Spirifer duplicostata (rare). 



Lingula squamiformis, abundant in the shales. 



Orthis radialis (rare). 



37. The trap above referred to as overlying these strata is a pro- 

 jection or tongue, running down to the shore from the principal 

 mass above, which occupies a considerable area inland towards 

 Ascog lake, and is upwards of 100 feet thick. It is seen in the 

 summit of the cliffs on either side, the line of junction ascending 

 rapidly as it retires from the shore. These trap rocks at Ascog 

 derive their chief interest from being the repository of beds of lignite ; 

 a substance so rare in Scotland, that no well-marked beds occur on 

 the mainland, and but few in the other islands ; and these in 

 situations very difficult of access. A careful examination of this car- 

 bonaceous deposit was suggested by the statement of Dr. MacCulloch, 

 that some of the beds occurring here were unlike any he had seen in 

 his survey of the Western Islands. 



The principal bed is situated in the face of the cliffs above the road, 



