206 Proceedings of the Koyal Society of Edinburgh. [Sess. 
associated with the Calderwood Cement Limestone. Here, again, we have 
an estuarine and marine type in association, the former represented by 
the shales containing Posidonomya corrugata, scales, plates, and bones of 
fishes of an estuarine character, and land plants, the marine type by the 
cement limestone full of brachiopods and other purely marine forms. A list 
of the more characteristic species of this horizon is given on pp. 188-189. 
In the West of Scotland the principal features of the Top Marine Band 
are a bed of shale which is simply a mass of Lingula squamiformis 
and limey shales, sometimes passing into limestone largely made up of 
single ossicles of a small crinoid. At certain localities the calmy lime- 
stone or calcareous shales are largely made up of the crushed valves of 
Schizophoria resupinata and other small brachiopods, with which is often 
associated the polyzoan Ceriopora interporosa, which at certain localities 
occurs in great abundance. Another outstanding feature of this horizon 
is the abundant occurrence in the sandstones and limestones of the marine 
alga Spirophyton cauda-galli. 
XIY. Position in the Avonian Sequence. 
If the foregoing correlation of the Dunbar Section with the Hurlet 
Sequence prove to be the correct one — and it seems to us to rest upon a 
fairly strong foundation of facts — it enables us to form some idea of the 
relationships of the Lower Carboniferous Limestone Series of the Midland 
Valley of Scotland to the Carboniferous Limestones of the North of 
England. In the year 1898* the late Mr William Gunn of the Geological 
Survey showed that the group of the lower Scottish limestones about 
Dunbar and round the Midlothian Coalfield does not represent any part 
of the mountain limestone of Yorkshire, but is the equivalent of the upper 
part of the Yoredale Series of Phillips, and which were included by him 
in the Millstone Grit. He identified one of the Longcraig Limestones, or 
perhaps the set of them (it does not seem quite clear which), as the 
equivalent of the Eel well Limestone of North Northumberland and the 
Five Yards Limestone of Weardale and Teesdale. The Skateraw Limestone 
(probably the Middle Skateraw) was considered by him to be the equivalent 
of the Acre Limestone of Lowick, and a still higher member of the Dunbar 
Group (probably the Chapel Limestone) he regarded as the equivalent of 
the Dryburn Limestone of Lowick and the Great Limestone of Teesdale 
and Weardale. 
Professor E. J. Garwood in his paper on the Lower Carboniferous 
* “Correlation of the Carboniferous Rocks of England and Scotland,” Geol. Mag., 
p. 342, 1898 ; also Trans. Edin. Geol. Foe., vol. vii, p. 361, 1899. 
