Fresidenfs Address. 41 



latisswuis,^ and forms from tliis circumstance a good horizon 

 for surveying purposes. This bed is well displayed at Joppa 

 quarry, near Edinburgh, and also on the banks of the North 

 Esk river, at Valleyfield, near Penicuik. Again in the shale 

 above the Hosie lime at Campsie a small Chooictes was found 

 in millions by Mr John Young, and believed to be a variety 

 of the common Carboniferous species.-|* 



Attention has of late been directed to the collecting of the 

 youngest possible stages of the species found in Scotland, the 

 specimens varying from the size of a pin's head to that of 

 one or two lines in diameter. Such investigations have been 

 chiefly carried out by Messrs R. Craig, of Beith, and J. 

 JSTeilson, j un., of Glasgow. 



Certain beds in the Lower Limestone group of Ayrshire 

 are particularly noticeable for their yield of these small 

 Brachiopoda. For instance, at Dockra cjuarry, Mr Neilson 

 states " that these little shells constitute the chief feature of 

 the deposit there, indeed hundreds of specimens may be 

 collected from one teaspoonful of the washed material." | 

 Another interesting point connected with this subject 

 has been noticed by Mr Craig, in the abundance of 

 young examples in a certain deposit, and the comparative 

 absence of the mature shells of the same species from the 

 bed.§ 



Many Carboniferous Brachiopods appear to pass through 

 endless varieties, a good example being the common Sjnrifera 

 trigonalis. A very interesting paper has been written by 

 Mr J. Young on this subject, " Notes on the Occurrence and 

 Distribution of SpirifcTa trigonalis, and its varieties in the 

 Limestone Strata of the Coalfields of the West of Scotland." || 

 Mr Young considers that the large number of varieties thrown 

 off by the typical form are probably produced by descent 

 from one original type. aS'. trigonalis commences to show 

 itself in the lowest marine bed of the Carboniferous lime- 

 stone, and ranges upwards to the millstone grit. Further- 



* Mem. Geol. Survey, Scotl., Expl. 23, 1873, p. 82. 



+ Davidson, Mon. Garb. Biach., p. 187. 



X Davidson, Suppl. Carb. ]\Ion., 1880, p. 264. § Ibid. 



II Proc. Nat. Hist. Soc, Glasgow, 1876, iii., pt. 1, p. 37. 



