18 Proceedings of the Royal Physical Society. 



represents another depression of the land surface, and the 

 return of marine organisms forming the first stage in the 

 same cycle of physical conditions. It is evident that during 

 the deposition of the middle coal-bearing group, where the 

 limestones are absent, that the land could only have under- 

 gone a limited submergence after the accumulation of the 

 vegetable matter. The depth of water was not sufficient to 

 allow the marine organisms to migrate to those areas of 

 deposit. From the data now adduced it is manifest that the 

 existence of marine organisms in any particular area of 

 deposit depended solely on the nature of the physical con- 

 ditions, and when we remember that the same cycle of 

 physical conditions must have been repeated again and again 

 during the Carboniferous Limestone formation, we may be 

 able to appreciate the vast amount of evidence in support of 

 the ingenious doctrine propounded by Barrande. 



After the deposition of the Millstone Grit the overlying 

 Coal-measures point to fresh- water conditions or land sur- 

 faces. The latter were in all probability more extensive 

 than those in the Carboniferous Limestone formation, and 

 may have been connected with continental areas. This 

 period was characterised by an incursion of the slowly 

 migrating plants, which replaced to a large extent those met 

 with in the lower coal-bearing series. It is a remarkable 

 fact that some of the plants belonging to the true Coal- 

 measures had gained access into the Scottish area of deposit 

 even in Lower Carboniferous time, for several have been 

 recognised in the Canonbie coal seams. Such a phenomenon 

 points to the conclusion that the Coal-measure flora existed 

 outside the Scottish area before the deposition of our Car- 

 boniferous strata, and that it would therefore be unsafe to 

 regard the Scottish beds as contemporaneous with those of 

 the continent of Europe. 



While carrying out researches with the object of collecting 

 spores and seeds in the coal seams of the Lothians, my col- 

 league, Mr Bennie, has obtained interesting evidence in proof 

 of the existence of numerous land animals on these old land 

 surfaces. He has shown that every little coal seam contains 

 innumerable fragments of the tests of scorpions and Euryp- 



