188 THE CANADIAN NATURALIST. [Vol. vi. 



ON THE " COLONIES " OF M. BAREANDE. 



By Henry Alleyne Nicholson, M.D., D.Sc, M.A., Ph.D., F.R.S E., 

 F.G.S., &c. Professor of Natural History and Botany in Univer- 

 sity College, Toronto. 



The doctrine of " Colonies," propounded by M. Barrande, has 

 been long before the palgeontological world, and is known, at any 

 rate by name, to all students of geology. It is doubtful, however, 

 if there is as clear a comprehension of this subject as its import- 

 ance would render desirable ; and it may, therefore, be of inte- 

 rest to discuss briefly the leading facts upon which this theory is 

 based. In so doing, I shall take the necessary details from M. 

 Barrande's " Defense des Colonies," published in 1870, one of 

 the most valuable of the many palgeontological works of this dis- 

 tinguished observer, and I shall confine myself chiefly to a rtsumi 

 of the facts therein recorded and the deductions drawn therefrom. 



I. Sub-divisions of the Silurian Rocks of Bohemia. 



The Silurian Rocks of Bohemia are described by M. Barrande 

 as occupying an elliptical basin, the long axis of which has a 

 N.E., and S.W. direction, and a length of 148 kilometres. The 

 breadth of the basin increases gradually in passing from the N.E. 

 to the S.W., its minimum breadth being about 30 kilometres, 

 and its maximum about 74 kilometres. The Silurians of this 

 basin repose upon granitic and gneissic rocks, and dip inwards 

 towards a central line. The fossiliferous beds of the entire basin 

 occupy a far from considerable superficial area ; and their extent 

 — supposing them not to have been much denuded — would assign 

 to the Silurian sea of Bohemia an area not exceeding 1-60 of the 

 superficies of the Adriatic. 



The Silurian rocks of the entire basin admit of separation into 

 two primary divisions, an Inferior and a Siqjerior division, cor- 

 responding respectively to the Lower and Upper Silurian Rocks 

 of Sir Roderick Murchison. The Inferior Division is composed 

 principally of schists and quartzites ; or, as we should say, slates 

 and grits or graywackes, and is wholly destitute of calcareous 



