164 SUBDIVISIONS OF THE CARBONIFEROUS SYSTEM 
No difficulty has been experienced in separating the various 
geological formations in the Counties of Nova Scotia mentioned 
above, nor of understanding their taxonomic relations. The most 
excellent work of Mr. Hugh Fletcher, of the Geological Survey 
of Canada, who kindly furnished me with maps and plans of the 
region in question, shows clearly the true and natural order of 
sequence of the formations. The main question at issue, how- 
ever, has been where to place the series of sediments hitherto 
known, and designated by Mr. Hugh Fletcher as the “ Rocks of 
Union and Riversdale”: in the Carboniferous or in the Devonian 
system. Mr. Fletcher would place them in the Devonian. I 
include them as formations in the Carboniferous system (and 
would also classify in the same system the red rocks of Mispee 
and the Lancaster fern-ledges of New Brunswick, which hold 
much the same flora and fauna). The various formations of the 
Carboniferous system do not form an unbroken succession of 
sedimentary strata in the disputed region either of Pictou, Col- 
chester and adjacent counties. Great breaks and unconformities 
appear on every hand. 
It may not be considered out of place here to look for a 
moment at some of the principles involved in such questions as 
arise inthis problem. Portions of formations constituting cycles 
of sedimentation or of constructive forms, marking peculiar 
physical conditions of deposition, followed by periods of erosion, 
and subsequent depositions, occur at various horizons, and were 
it not for their entombed faunas it would be most difficult to 
state in which of the subdivisions of the Palaeozoic column to 
place them. Where sedimentation as marked by cycles of con- 
structive forms is not continuous, the basis or principle upon 
which the separation of the different members of the series 
depends, must obtain in the paleontological evidence collected 
in the various members whose succession, though not perfect, 
is, nevertheless, known as to its order. 
Similarity in the types or organic forms found, assists one in 
uniting series of sediments as part and parcel of one system, just 
as dissimilarity enables one to separate series of sediments from 
