458 TRANSACTIONS OF SECTION C. 
« 
the long trough north-east of Alabama. J/esonacis has been obtained in the 
submarine depression at Lake Champlain, at Bonne Bay, Newfoundland, and at 
the north side of the Straits of Belle Isle. Hiliptocephalus has been recorded 
from the New York State. Olenellus has been found in Nevada, in Vermont, 
and in the North-West Highlands. All the genera now referred to may have 
migrated along the north-western shore of this trough. 
As regards the distribution of the genus Callavia, this form has been met 
with in Maine, in Newfoundland, and in derived pebbles in a conglomerate in 
(Juebec. Two species have been recorded in Shropshire. These forms probably 
moved along the southern shore of this sea from Wales to North America. 
Reference has already been made to the fact that, in the interval between 
Lower and Middle Cambrian time, in certain areas in North America the Lower 
Cambrian rocks were locally elevated and subjected to erosion. During this 
interval the southern end of the trough seems to have had no connection with the 
Mississippian sea, for in Middle Cambrian time, as already indicated, the 
Paradoxides fauna is found in the trough on the east side of North America, 
whereas on the west side it is represented by the Olenoides fauna. 
In Upper Cambrian time a great transgression of the sea towards the north 
supervened. The Dikelocephalus fauna is found on both sides of America, 
thus showing that the previous land barrier had been submerged. While this 
genus occurs in Wales and the Baltic provinces, it has not as yet been recorded 
from the North-West Highlands, but I quite expect that this discovery may 
be made at some future time. 
Along the northern side of the American trough clear-water conditions pre- 
vailed, owing to the northward recession of the shore-line, which led to the 
accumulation of a great succession of calcareous deposits, including the Beekman- 
town limestone, to which reference has alreaay been made. Schuchert, as 
already stated, has pointed out that, in the lower part of the Ozarkic (Upper 
Cambrian) system, in Minnesota and Wisconsin, the gasteropod genera, Holopea, 
Ophileta, and Raphistoma, are associated with two species of Dikelocephalus. 
This molluscan fauna is evidently the precursor of that of the Beekmantown 
limestone. It was probably from this central region of America that the cal- 
careous fauna of Beekmantown migrated to the submarine trough in the typical 
Champlain region, and through Newfoundland to the North-West Highlands 
of Scotland. 
The section at St. John, New Brunswick, where the Baltic and Welsh types 
of the Olenus fauna occur, shows that the southern shore-line of the trough must 
then have occupied much the same relative position as in Lower and Middle 
Cambrian time. In the same region the strata containing this fauna, with 
Peltura scarabaoides, and Dictyonema flabelliforme are overlain by dark shales 
with Arenig graptolites. These graptolite-bearing terrigenous deposits eventu- 
ally extended across the trough northwards, till, in Newfoundland, they came to 
rest on the Beekmantown limestones. 
In the Lake Champlain region, in the Chazy limestone, which there imme- 
diately succeeds the Beekmantown limestone without the intervention of the 
Arenig graptolite shale, there is a survival of the Beekmantown molluscan fauna 
with only such slight modifications as to indicate genetic descent. In the 
same trough the descendants of this fauna are to be found in the Trenton 
limestone. 
In this connection it is worthy of note that the molluscan fauna and the 
corals of the Stinchar and Craighead limestones of Upper Llandeilo age in the 
Girvan district of the Southern Uplands have an American facies, as first 
suggested by Nicholson. The appearance of American types in these lime- 
stones may be accounted for in the following manner: Attention has already 
been called to the divergent types of sedimentation presented by the Upper 
Cambrian strata of the North-West Highlands, and of the South-East High- 
lands, at Stonehaven and Aberfoyle. In the former case there is a continuous 
sequence of dolomites and limestones, while in the latter we find a group, com- 
prising radiolarian cherts and black shales, associated with pillowy spilitic 
lavas and intrusive igneous rocks, indicating conditions of deposition at or near 
the limit of sedimentation. But, notwithstanding the different types of ‘sedi- 
mentation and the divergent faunas in the two areas, I believe that during the 
Upper Cambrian period, and probably for some time thereafter, continuous sea 
