THE GEOLOGICAL STRUCTURE OF THE CANONBIE COALFIELD. 845 



the group consists of fine decomposing basic tuffs and thin basic lava, in the midst of 

 which there is a zone of sediments, comprising black shales, oil shale, and black cherts, 

 followed by fine-grained calcareous shale of unique pakeontological importance. From 

 this horizon of calcareous shale a great variety of organic remains has been obtained, 

 including plants, ostracods, brachiopods, lamellibranchs, cephalopods, crustaceans, fishes 

 and land animals (scorpions and eurypterids). The extraordinary feature of the band 

 is the very large number of new genera and species gathered from this single exposure in 

 the Esk, which has made it one of the classic fossil-localities in Scotland. The discovery 

 was made by the skilled fossil-collector of the Geological Survey, Mr A. Macconochie. 

 From the fact that these sediments are both underlaid and overlaid by tuff, it is evident 

 that they are merely an episode in the phase of volcanic activity on this horizon. 

 Indeed, it is worthy of note that this rich palseontological zone, though carefully sought 

 for, has not been found at any other locality. 



Though a great variety of forms has been obtained from the Glencartliolm shales, it 

 is interesting to observe that they are not equally distributed through the successive 

 layers. For example, the fishes are usually found underneath a band in which 

 Orthoceras is a conspicuous fossil. The scorpions and plants usually occur together in 

 a separate bed, while the crustaceans are found in association with the fishes. The ferns 

 are usually represented by separate fronds, and they are often covered with a calcareous 

 incrustation, as if they had floated about in concentrated calcareous solutions before 

 becoming embedded. No coal-seam nor root-bed appears in this zone. The remains of 

 the Crustacea seem to have been filled in with orbicular calcite during decomposition, as 

 if they had lain in water highly charged with calcium sulphate. This feature seems to 

 point to lagoon conditions, as if arms of the sea had been temporarily cut off from the 

 open ocean and subjected to desiccation. Strings of Spirorbis and of an adherent 

 brachiopod shell are often found, fixed to carbonaceous stems of decomposing plants. 

 Some of the bands of shale are covered with the chitinous tubes of marine worms. Sea- 

 weeds are represented by Bythotrephis. 



In view of the evidence regarding the conditions of entombment of the organic 

 remains, it is highly probable that the Glencartliolm shales may have been deposited 

 in a muddy creek, shut off at intervals from the open ocean. 



In his recent valuable paper " On the Distribution of Fossil Fish-remains in the 

 Carboniferous Rocks of the Edinburgh District,* Dr Traquair states that out of the 

 large number of fishes found at Glencartliolm, only one (Tristychius minor) is found 

 in the Lower Carboniferous rocks of central Scotland. But it is quite possible, when 

 the divisions of the Lower Carboniferous rocks in Berwickshire, the Lothians, Fife, and 

 the West of Scotland have been thoroughly searched, some forms, now restricted to 

 Glencartliolm, may be found. The present revision of the coalfields furnishes an 

 opportunity of testing this question. In connection with this point it may be 

 observed that some of the crustaceans which were at first thought by Dr Peach 



* Trans. Roy. Soc. Edin., vol. xl. p. 687. 



