THE GEOLOGICAL STRUCTURE OF THE CANONBIE COALFIELD. 



843 



Avieulvpccten interstitialis, Phill. 



„ macroiis, M'Coy. 



Modiola Macadami, Portl. 



„ sp. 

 Myalina siiblamellosa, Eth. jnr. 

 Nucidana attemicda, Flem. 

 Nucida stilla, M'Coy. 

 P rotoschizodus axiniformis, Portl. 

 Sanguinolites costcllatus, M'Coy. 



„ striato-lamellosus, De Kon. 



. S P- 

 Tcllinomorpha ciinciformts, De Kon. 

 Edmondia josepha, De Kon. 



Ed inondia. pectanculus. 

 Entolium Sowerbyi, M'Coy. 

 Loxoncma curvilinca, Phill. 



sp. 

 Murchisonia Verncidiana, De Kon. 

 Macrocheilus acut'us, Sow. 

 Naticopsis plicistria, Phill. 

 Ivania (Elewotomaria) Ivani, Lev. 

 Comdaria quadrisidcata, Sow. 

 Discitoceras (Discites) sulcatus, Sow. 

 Orthocerus attenuatwm, Flem. 

 „ linealc, De Kon. 



sp. 



Above the horizon of the marine limestones of Thorlieshope the strata indicate a 

 reversion to estuarine conditions. Immediately below the Fell sandstones, however, a 

 w T ell marked and persistent band of limestone appears, charged with a peculiar calcareous 

 organism, named Mitcheldeania gregaria by the late Professor Alleyne Nicholson. 

 It occurs in the well known limestone at Kershopefoot and at Kidds Linn. 



Though land plants occur more or less frequently throughout the group, it is only 

 occasionally that a true land surface is indicated by an under-clay with underground 

 rhizomes such as Stigmaria in place. One thin coal-seam, however, about ten inches 

 thick, is found near the top of the Cementstone group, under Peel Fell on the Scottish 

 side, which is the lowest known coal-seam on the border. The characteristic ferns of 

 the group are Calymmatotheca (Sphenopteris) affinis and C. bifida ; at Tarrasfoot 

 Rachopteris incequilatera also occurs. 



The fishes found in the Cementstone group are not of common occurrence, and, as 

 might be expected, are almost wholly of an estuarine character. These have been 

 submitted to Dr Traquair for determination, who has identified the following forms 

 in the collection : Strepsodus, sp.. Rhadinichthys Macconochiei, Traq., and Styracopterus 

 ftdcratus, Traq. In the marine limestone zone of Thorlieshope and Larriston Burn 

 palatal teeth of marine sharks have been obtained. 



Land animals also occur in the form of Scorpions, while Myriapods belonging to 

 more than one genus have been found in rocks of this horizon in the basin of the Tweed 

 near Coldstream. 



From the peculiar lithological characters of the Cementstone group, the distribution 

 of the beds is comparatively clear in Eskdale and Liddisdale. In the Esk and in the 

 lower part of the basin of the Tarras Water they form a simple outcrop overlying the 

 Whita sandstone, and dipping generally in a southerly direction at an average angle of 

 about 20°. When followed north-eastwards to the Tinnis Burn they are spread over a 

 wide area, owing to repetition by folding, and occupy a basin three miles in width, 

 which extends up the Hermitage Water towards the northern margin of sheet 11 of the 

 one-inch map of Scotland. On its eastern side this basin is truncated by a powerful 

 north and south fault which brings the Cementstone group successively in contact with 

 the Upper Silurian inlier of Arnton Fell near Riccarton, and with the Upper Old Red 

 TRANS. ROY. SOC. EDIN., VOL. XL. PART IV. (NO. 32). 6 k 



