38 PROCEEDINGS OF THE 



only other organisms met with in the Scottisli Okl Eed are 

 crustacean and plant remains. Of the Crustacea, the genus 

 JEstheria affords evidence of fresh-water conditions. We find no 

 remains of corals, crinoids, or molluscs, such as characterize the 

 marine strata of the Devonian forma,tions of other countries, and 

 which are believed to be the marine equivalents in time of the Old 

 Eed of Scotland. The evidence afforded by the organisms, and by 

 the prevailing red colour of the formation, favours the assumption 

 that the whole series of beds were accumulated in a great fresh- 

 water lake or lakes, but in which the waters may have been at 

 times slightly brackish. 



In the east of Scotland, in the calciferous sandstone series that 

 overlies the Old Eed Sandstone, we meet with, at intervals in the 

 strata, evidence of the return of the sea, as indicated by the 

 occurrence of certain characteristic marine fossils of the Car- 

 boniferous limestone period, which there make their appearance 

 for the first time, so far as known to us. 



In the west of Scotland, the calciferous sandstone series forming 

 the lowest division of our Carboniferous system, is represented by 

 a series of fresh-water strata, known as the Ballagan group, in 

 which no characteristic marine fossils have yet been found. 

 Overlying this group, we have a great thickness of trappean or 

 volcanic rocks, which build up the Campsie, Kilpatrick, Eenfrew, 

 and Ayrshire hills ; these in their turn are succeeded by strata 

 belonging to the lower Carboniferous limestone period, in which 

 we have abundant evidence of those alternate changes of conditions 

 — from lakes, with fresh-water strata, to land surfaces, with 

 forests of vegetation, as represented by our coal-seams; and from 

 these to deep sea bottoms, with their growths of corals, crinoids, 

 shells, shark-like fishes, and other characteristic marine forms. 



Having stated this much regarding the ])alaeontological character 

 of the Old Eed Sandstone and Carboniferous strata, as indicated 

 by their fossils, I come noAv to call your attention shortly to a 

 group of the Sjnrifera, found in the marine limestone strata, 

 belonging to the well-known and common species, Sjnrifera 

 trifjonalis, Martin, and the variety, S. Usidcata, Phil. These two 

 forms present us with several variations in shape, which in some 

 cases seem to be peculiar to certain localities, and to the strata of 

 different geological horizons j and as the species ranges from the 

 lower beds of tlic limestone series, in the west of Scotland, up to 



