President'' s Address. 39 



Mollusca in tlie Caiboiiiforoiis Liinostoiio series, liaviiig 

 assisted in tlie formation of many of tlio bands of limestone 

 into which that formation is split up in Scotland. For 

 instance, Mr R. Craig states that some of the upper lime- 

 stones of the Lower Carboniferous Limestone Group in the 

 Dairy district are almost built up of the remains of Pro- 

 dnctus, Spirifer, and TcrebrcUula* 



The Bracliiopoda further possess, through the eminent 

 services of Mr T. Davidson, F.K.S., the advantage of long 

 and continuous investigation into their structure and dis- 

 tribution. 



At present some sixteen or seventeen genera, and about 

 fifty-nine or sixty species have been described from Scotch 

 localities, as compared with one hundred and seventeen 

 species in the English, and eighty-four in the Irish Carboni- 

 ferous limestone.i* 



Brachiopoda grow continuously less ^and less plentiful as 

 we ascend in the Carboniferous series. This holds good both 

 in England and Scotland. They flourished essentially during 

 the deposition of the Carboniferous Limestone and its accom- 

 panying shales. J 



Of the fifty-nine species several are now known to pass 

 upwards into the Permian system of England. It is a point 

 of much interest to watch day by day the increased number 

 of forms which Palaeontology indicates as common to the 

 two formations. 



Although some of the Scotch Brachiopods vie in size with 

 specimens from the thick masses of limestone in other parts 

 of the British Islands, the individuals found in Scotch beds, 

 are, as a general rule, much dwarfed in size, but frequently 

 more perfectly preserved. This is probably to be accounted 

 for by less favourable conditions of existence.§ 



All the genera found in the west of Scotland are met with 



*^ "On the Fossils of the Upper Scries of the Lower Carboiiiferous Limestones 

 in the Btith and Dairy Districts of ISTorth Ayrshire" (Trans. Geol. Soc, 

 Glasgow, 1879, vi., pt. 1, p. 4). 



t I am under obligations to Mr Davidson for these details. 



t Davidson, Garb. Mon., 1857, p. 3. 



§ Davidson, Geologist, 1860, iii., p. 237 ; Yonng and Armstrong, Catalogue, 

 p. 36; Somervail, Trans. Geol. Soc, Edinb., 1877, iii., p. 70. 



