40 
It will be noted from the preceding table that the sections 
at Ottawa and MacLaren landing are not as fossiliferous as 
that at Rockland, owing, partly, to the absence of the shale 
layers which at Rockland hold an abundant and well-preserved 
fauna. Not only are there fewer species, but very few species 
are abundant. 
The absence df an echinoderm fauna in the Trenton beds 
in these sections is explained by the fact that the usual echino- 
derm-bearing strata in the vicinity of Ottawa and in the Trent 
valley are higher than the Rockland beds. 
In the quarry at Rockland the Trenton beds lie conform- 
ably upon the Black River so that there appears to have been 
no emergence of the sea-bottom during the transition to the 
Trenton sea. Additional evidence of continuous deposition is 
afforded by the gradual change in the fossil content of the strata. 
A few specimens like Tetradium fibratum found in the upper 
part of the Lowville persist into the Trenton. The same may 
be said of Strophomena filitexta, but in both cases the height of 
the curve is reached in the Leray beds of the Black River. In 
layer No. 4 of the Black River there is a large Tetradium measur- 
ing 2 feet or more in diameter. Higher up in the Trenton beds 
the species is represented by specimens a few inches in diameter. 
Within the Black River there is, as is to be expected, a group of 
fossils confined to the Lowville, such as Tetradium cellulosum ; 
and a group confined to the Leray beds, for example, Piano- 
dema subaequata; while there are others which are found in both 
divisions, as Orthoceras multicameratum. Comparing the fossil 
content of the Black River with that of the Trenton we find 
evidence of the same condition, though different in degree. 
Triplecia extans , Hormotoma trentonensis, Calymene senaria , 
and others are confined to the Trenton beds. Plectambonites 
sericeus, on the other hand, makes its first appearance in the 
Leray beds of the Black River. Though this is generally fairly 
frequent in the Leray beds elsewhere, the specimens found here 
were few and far between, though they are quite common in the 
Trenton beds. The same history holds good for Rafinesquina 
alternata and others. There is, then, in the upper beds of the 
