PRESIDENTIAL ADDRESS. 457 
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evidence that the pre-Torridonian Jand was one of high relief. As the Tor- 
ridonian sediments form part of a continental deposit it may be inferred that 
the Archean rocks had a great extension in a north-westerly direction. The 
increasing coarseness of the deposits towards the north-west suggests that the land 
may have become more elevated in that direction. At any rate, the pile of Tor- 
ridonian sediments points to a subsidence of the region towards the south-east, 
and probably to a correlative movement of elevation towards the north-west. 
The sparagmite of Scandinavia is an arkose resembling the dominant type 
of the Torridon sandstone; is of the same general age, and has evidently been 
derived from similar sources in the Scandinavian shield. In eastern North 
America coarse sedimentary deposits form part of the newer Algonkian rocks, 
which are still to be found rising from underneath the Cambrian strata in the 
region of the Great Lakes. These materials were obtained from the great 
Canadian shield, which must have formed a large continental area during their 
deposition. 
It is reasonable to infer that these isolated relics of old land surfaces were 
united in pre-Torridonian time, thus forming a continuous belt from Scandinavia 
to North America. During the period which elapsed between the deposition of 
the Torridon sandstone and the basement members of the Cambrian system a 
geosyncline was established which gave rise to a submarine trough, trending in 
an east-north-east and west-south-west direction, both in the British and North 
American areas. In the latter region it extends from Newfoundland to 
Alabama, its south-eastern limit being defined by the old land surface of Appa- 
lachia. The extension of this Appalachian land area in a north-east direction 
beyond the limits of Nova Scotia and Newfoundland was postulated by Dana 
and other American writers. This geosyncline remained a line of weakness 
throughout paleozoic time, both in Britain and North America, which resulted 
in the Caledonian system of folding in Britain, and in the Taconic, Appalachian, 
and Pennsylvanian systems in North America. Hence it is manifest that the 
original shore-lines of this trough are now much nearer each other than they 
were in Cambrian time. 
The Cambrian rocks of the North-West Highlands were laid down along the 
north-west side of this trough during a period of subsidence, for the great 
succession of Durness dolomite and limestone, with little or no terrigenous 
material, is superimposed on the coarser sediments of that formation. On the 
other hand, the Cambrian strata of Wales seem to have been deposited along the 
southern limit of this marine depression. The Archean rocks that now con- 
stitute the central plateau of France may have formed part of its southern 
boundary. The extension of this land area towards the north-east may have 
given rise to the barrier that separated the Baltic life-province from that of 
Bohemia, Sardinia, and Spain. In my opinion, this southern land area in 
Western Europe was continuous across the Atlantic with Appalachia. For the 
life sequence found in the Cambrian rocks of New Brunswick is practically 
identical with that of Wales and the Baltic provinces, thus showing that there 
must have been continuous intercourse between these areas. Along this shore- 
line the migration of forms seems to have been from Europe towards America. 
On the other hand, along the northern shore the tide of migration seems to 
have advanced from America towards the North-West Highlands. The question 
naturally arises, what cause prevented the migration of the forms from one shore 
of this trough to the other? American geologists are of opinion that this is 
probably due to the existence of land barriers; but, in my opinion, it can be 
more satisfactorily accounted for by clear and open sea, aided by currents. 
The south-western extremity of the American trough in Lower Cambrian 
time opened out into the Mississippian sea, which was connected with the 
Pacific Ocean, and stretched northwards towards the Arctic regions. Reference 
has already been made to Walcott’s discovery in Nevada of the primitive 
trilobite Nevadia Weeksi, from which he derives both branches of the 
Mesonacide, one branch linking Nevadia, through Callavia, Holmia, and Wan- 
neria, with Paradoxides, the other connecting Nevadia with Olenellus, through 
Mesonacis, Elliptocephalus and Pedumias. 
In Nevada the genus Holmia, as already shown, is associated with the primi- 
tive type Nevadia. Wanneria is found in Nevada, in Alabama, and in Pennsyl- 
yania, thus showing that this genus is common to the Mississippian sea and to 
