President's Address. 13 



The Upper Old Eed Sandstone strata of Scotland are 

 separated from all older formations by a strong unconforma- 

 bility, indicating an upheaval of the continental area, and 

 prolonged denudation of the old land surface, composed of 

 the crystalline schists, together with Silurian and Lower Old 

 Eed Sandstone strata. On this land surface were still to be 

 found some of the Old Eed lakes, much reduced in size, but 

 still containing a few of the descendants of the denizens of 

 the Lower Old Eed waters. In these land-locked basins the 

 breccias, sandstones, and shales forming the upper division 

 of the system were accumulated, and in these deposits were 

 entombed the remains of such fishes as Holoptychius and 

 Pterichthys major, while in the open sea the Carboniferous 

 Limestone formation was being built up by marine animal 

 life. As the land in the northern areas gradually sank, the 

 lacustrine and littoral deposits were succeeded conformably 

 by estuarine and marine strata of Lower Carboniferous age, and 

 a much newer facies of fish fauna followed the Old Eed types. 

 This seems to me to be the explanation of the peculiar rela- 

 tions of the Upper Old Eed Sandstone to the Lower Carboni- 

 ferous rocks of Scotland. Sometimes the Upper Old Eed 

 strata are separated from the Lower Carboniferous rocks by 

 an important development of volcanic rocks ; but when this 

 volcanic zone is absent, it is difficult to draw a boundary 

 line between them. Notwithstanding this apparent passage, 

 there is a wide divergence in the respective fish faunas, the 

 Upper Old Eed forms being more nearly allied to those of 

 the lower division of the system than to the overlying Car- 

 boniferous species. This remarkable palsoontological break 

 in a conformable series of strata can be satisfactorily ex- 

 plained if we regard the Upper Old Eed fishes as the sur- 

 vivors of an older fauna, still confined to land-locked basins, 

 while the Carboniferous forms suddenly gained access to the 

 Scottish area from the open sea, where they had developed at 

 a much more rapid rate than their less favoured relatives. 



The relations of the Lower Carboniferous rocks of Scotland 

 to the Carboniferous Limestone formation of Central England 

 have been satisfactorily proved by the researches of the 

 officers of the Geological Survey of the latter kingdom. 



