180 Proceedings of the Royal Society of Edinburgh. [Sess. 
Ft. In. 
B. 7. Blackbyre Limestone, Brachiopods and Corals . . . ,10 
6. Coal ............ 1 
5. Holly bush Sandstone, with Lady Ann coal in the middle . .150 
4. Shale, with limey band full of Rhynchonella pleurodon . . 8 
A. 3. Hollybush Limestone, Productus latissimus and Lithostrotion . 4 
2. Coal 12 
1. Sandstones, marls, and fireclays . . . . . .... 
In the above table is shown the principal limestone horizons exposed 
in the neighbourhood of Hurlet. At the bottom of the section is the 
Hollybush Limestone, formerly wrought near the farm of that name. 
This limestone has a thickness of 4 feet, and is the lowest well-marked 
calcareous horizon to be met with in the Hurlet district. As we have 
elsewhere pointed out, it is characterised by the presence of bands of 
Lithostrotion and solitary corals with large Proclucti , including P. giganteus, 
P. latissimus, P. punctatus, and P. semireticulatus. Other brachiopods 
present are Spirifer trigonalis and Seminula ambigna. In the calcareous 
shale overlying the limestone there is a bed which is simply a mass of 
crushed specimens of Rhynchonella pleurodon* 
At a distance varying from 10 to 20 fathoms above the Hollybush 
Limestone lies the Blackbyre Limestone, which can be seen in the railway 
cutting near the farm of that name a mile to the south-west of Hurlet. 
At this locality the upper part is composed of small encrinite fragments, 
while the lower is slabby and almost entirely composed of small brachio- 
pods, principally Productus longispinus Sow. and Spirifer dtiplicicosta 
Phill. It is also important to note that plant remains are numerous, 
especially in association with the brachiopod bed in the limestone.*)* The 
Blackbyre Limestone was also formerly worked at Blackhall, where the 
evidence goes to show that it presents three distinct palaeontological types, 
the lower part being characterised by the presence of large brachiopods 
with bands of Lithostrotion ; the middle part being slabby, with immense 
numbers of small brachiopods ; while the upper part is fine grained, 
approaching the estuarine type, which was worked at Gallowhill, near 
Arkleston, about the beginning of the last century, and which yielded 
to Dr Scouler the type specimens of Dithyrocaris testudinea and 
D. tricornis. J 
The Baldernock Limestone can be seen only in the Arkleston rail- 
way cutting, in which it occurs in three seams full of entomostraca 
* See Trans. Geol. Soc. Glasgow , vol. xv, p. 206. 
f Ibid., p. 207. 
7 Ibid., vol. xvi, p. 46. 
