1858.] DAWSON ^LOWEE COAL-MEASTJEES. 75 



1846*. Those described bj Mr. Binneyt and by Professor Hark- 

 ness J may have been produced by similar animals, of the same 

 geological age; and the far more ancient impressions from the 

 Longmynds, described by Mr. Salter §, much resemble those deli- 

 neated in fig. 7. In the I^ova Scotia coal-measures these marks 

 appear to be characteristic of the littoral zones (often probably of 

 great extent, owing to the flatness of the bottom) which intervened 

 between the land (or the coal-swamps) and the open waters inha- 

 bited by Brachiopods and Corals. 



Mollusca. — A small TJnio-like species from Parrsboro' is the only 

 representative of this province of the animal kingdom, that I have 

 found. It is not distinguishable from species found above the 

 marine limestones ; but this peculiar form of bivalve is confined to 

 the plant-bearing beds, and does not occur ia the strictly marine 

 parts of the system. It was probably a fresh- or brackish-water 

 shell. 



Markings. — On the surfaces of the beds at Horton there are many 

 singular markings, different from those which resemble trails of 

 Annelids. Most of them are mere scratches, perhaps of drift wood, 

 or of fins of fishes. One of the most curious forms is a furrow, 

 having on each side a series of transverse markings, which may 

 have been caused by the feet of Crustaceans (fig. 8). At the ter- 

 mination of such tracks there is usually a brush of curved scratches, 

 inclined to one side, as if the creature had raised itself from the 

 bottom to swim off. 



These markings, and the numerous smooth and distinct strata- 

 surfaces at Horton, show that the process of deposition was slow and 

 interrupted ; and it is probable that many of these surfaces, espe- 

 cially those covered with fish-scales, long formed the bottom of clear 

 water tenanted by fishes. On the other hand, occasional beds of 

 coarse sandstone and thick imperfectly-bedded shales, and the pre- 

 sence of beds with erect trees, indicate occasional deposition of large 

 quantities of sediment and important changes of level. In these 

 respects the lower coal-measures resemble those higher in the 

 system: but the presence of subaquatic conditions was greater in 

 the former; and while, on the one hand, the oceanic conditions 

 of the marine limestones with Brachiopods and Corals are absent, 

 on the other hand the terrestrial surfaces of the middle coal-period 

 are rare. The peculiar character of these beds, in reference to the 

 life of the period, is that they afford the first traces of its plants 

 and shore- animals, and that they show us the inhabitants of swampy 

 estuaries and forest-clad river-valleys mingled with the remains of 

 fishes that may have occasionally visited the surf- washed coral-reefs 

 of the distant sea. 



The lower coal-measures contain no valuable beds of coal. Their 

 sandstones are sometimes quarried for building-purposes ; and their 



* Quart. Jom'n. Greol. Soc. vol. ii. p. 132. 

 t Trans. Lit. Scien. Soc. Manchester, vol. x. 

 \ Edinb. New Phil. Journ. new series, vol. i. 

 § Quart. Journ. Geol. Soc. vol. xiii. p. 199. 



