Professor Nicholson on the Gitelph Limestones. 45 



Wednesday, 11th February 1^,75. — David Grieve, Esq., President, 

 in the Chair. 



The following gentleman was balloted for and elected a Resident Member : 

 John Goldie, Esq., H.M. Register House. 



The following donations were laid on the table, and thanks voted to the 

 donors : 



1. Proceedings of the Royal Society, Vol. XXIII., No. 157.— From the 

 Society. 2. Proceedings of the Linnean Society, Vol. XIV., No. 78. — From 

 the Society. 3. Proceedings of the Geologists' Association, Vol. II., No. 1. 

 — From the Association. 4. Transactions of the Manchester Geological 

 Society, Vol. XIII., Parts 6 and 7.— From the Society. 



The following communications were read : 



I. — On the Gitelph Limestones of North America, and their 

 Organic Beniains. By H. Alleyne Nicholson, M.D., 

 D.Sc, F.R.S.E., Professor of Biology in the Durham 

 University College of Physical Science, ISTewcastle-on- 

 Tyne, Corresponding Membei^. 



In this communication the author described the deposits 

 which form the uppermost portion of the Niagara Formation 

 (Wenlock Series) of North America. The deposits in ques- 

 tion are typically developed in western Ontario, where they 

 are known as the " G-uelph Formation," from their occurrence 

 in full force near the little town of Guelph. Lithologically, 

 the Guelph Formation consists of magnesian limestones, 

 usually of a buff or yellow colour, sometimes highly crystal- 

 line, but very commonly of an exceedingly porous texture, 

 owing partly to the existence of drusy cavities, and partly to 

 the numerous vacant spaces left by the weathering out of 

 organic remains. In the State of Ohio, all the limestones of 

 the Niagara Formation, with the exception of the celebrated 

 " Dayton Stone," are magnesian, and the Guelph limestones 

 are therefore not marked off from the lower beds by any dis- 

 tinctive peculiarity of a lithological nature. The summit of 

 the Niagara Formation in Ohio is, however, formed by a 

 group of dolomites, which can be unhesitatingly identified 

 with the Guelph Formation of Canada, not only by the pre- 

 cise similarity in mineral characters, but also by the identity 

 of organic remains. The Ohio geologists term these beds the 



VOL. IV. F 



