INTRODUCTION. 
61 
Sir William Logan has obtained from strata of this age, in Gaspe, frag¬ 
ments of the trunk of a tree several inches in diameter; and the 
abundant distribution of plants in that region indicates a proximity to 
their source, or that they are now imbedded in the soil where they grew. 
In the Coal measures proper, we find a similar state of things, with 
the mass of material much greater, the remains of a former flora 
extremely abundant and widely diffused, and the indications still 
stronger that, to a great extent, the area occupied by these strata was 
the land on which the plants flourished ; that they were destroyed by 
successive inundations or submergences, when the overflow of the 
waters bore with them the coarser materials which covered the pre¬ 
existing flora. 
In Nova-Scotia, with the profusion of land plants, there occur also 
remains of land shells : in Pennsylvania, and nearly all the more easterly 
Coal measures, land plants are abundant. 
These conditions, however, whatever they may have been, declined 
towards the west. The shore-derived material has extended only partially 
over the area; and there is in that direction not only a thinning of the 
entire mass, but also a paucity of plant remains. 
There is, moreover, a large accession of calcareous matter in that direc¬ 
tion. On comparing the sections of Professor Swallow, which are given in 
great detail, we find everywhere, but more particularly in the two upper 
divisions, a large proportion of calcareous material in the form of argilla¬ 
ceous shale, marl, etc., with numerous marine shells. The same is true of 
the Coal measures in the west : in Iowa, Illinois, and Indiana, we find an 
approach to this character. In Pennsylvania calcareous bands are few, and 
in extremely small proportion, increasing in Ohio and the west; while in 
Nova-Scotia, calcareous beds form a very insignificant proportion of the 
whole. 
This condition is only to be explained by supposing, as we have more¬ 
over evidence in proof, that the Coal measure sediments were driven 
westward into an ocean where there already existed a well marked marine 
fauna. This part of the ocean bed was subject to oscillations, and at times 
