Geological Society of Glasgow. 559 



Uplands, are, in default of more detailed palseontological data, most 

 safely referred to the Caradoc and Llandeilo rocks of Wales. 



In the discussion which followed, Mr. E. Hull, F.E.S., drew at- 

 tention to the poverty of the Scottish Silurian rocks in Limestones, 

 as compared with those of the Border districts of England and 

 Wales, where calcareous strata are more fully developed, and re- 

 marked that there was an apparent similarity in the distribution of 

 calcareous strata of the Silurian and Carboniferous rocks of the two 

 countries. In the latter case, the Carboniferous limestone was most 

 fully developed in central England, attaining in Derbyshire a thick- 

 ness of over 4000 feet, and gradually thinning away northward into 

 central Scotland. On the other hand, the sedimentary materials 

 augment in bulk towards the north-west, and in north Lancashire 

 attain a thickness of about 18,000 feet. Mr. Hull thought it pro- 

 bable that the Silurian sedimentary strata would be found to aug- 

 ment in bulk in a northerly direction, and in the inverse ratio of the 

 calcareous beds of the same formation. He believed that the cause 

 in each case (Silurian and Carboniferous) was the same, and that 

 these changes might be explained on grounds which Bischof had 

 hinted at in his "Chemical Geology" — that the existence of sediment 

 in the ocean is inimical to the formation of limestones. Applying 

 this doctrine to the cases of the Silurian and Carboniferous forma- 

 tions, and supposing the source of the sedimentary materials to have 

 lain in the region of the North Atlantic (then a continent), the ex- 

 planation of the tailing out of the calcareous beds towards the north 

 and north-west might, he thought, be found. 



II. — On the Upper Silurian Brachiopoda of the Pentland Hills, 

 and of Lesmahagow in Lanarkshire. By Thomas Davidson, Esq., 

 E.E.S., etc. Mr. Geikie had determined that the Upper Silurians 

 form the fundamental rocks of the Pentland chain, and are covered 

 unconformably by the Old Eed Sandstone, by felspathic traps of Old 

 Eed age, and by lower Carboniferous sandstones ; while their geo- 

 logical position was equivalent to the Ludlow rocks of England. 

 After the examination, however, of several thousand specimens of 

 the fossils, Mr. Davidson was of opinion that both the Ludlow and 

 the underlying Wenlock rocks were represented in the Pentland 

 Hills. The specimens of Brachiopods occur principally in the con- 

 dition of external casts and internal impressions — the shell itself 

 being rarely preserved. These observations were followed by a full 

 description of the species, about twenty-six in number. The re- 

 maining portion of Mr. Davidson's paper consisted of a description 

 of two species of Brachiopoda, Lingtila minima, Sowerby, and a 

 Bhynchonella, discovered by one of the members, Mr. Eobert Slimon, 

 in the Upper Silurian rocks of Lesmahagow. It was of great im- 

 portance that the fossils from the lower Palasozoic series of Scotland 

 should be correctly described and illustrated ; and with a view 

 towards furthering that object, he had gladly acceded to the request 

 made him by the President and by some members of the Society 

 that he should prepare for the Palgeontological Series of the Trans- 

 actions a series of descriptions and illustrations of our Scottish 

 Silurian Brachiopoda. J. A. 



