PRESIDENTIAL ADDRESS. 453 
in thickness (Durine group), has yielded two species of Hormotoma—viz., 
11. gracilis and H. gracillima—both of which occur in the two underlying groups. 
H. gracilis occurs in the Beekmantown, the Chazy, and the Trenton limestones 
of America. 
Before assigning any stratigraphical horizons to the fauna of the Durness 
dolomites, it is desirable, owing to the American facies of the fossils, to recapitu- 
late the evidence bearing upon the life of Cambrian time in North America. 
But the Cambrian life-history of Scotland would be incomplete without a brief 
reference to the recent discovery of fossils along the eastern border of the 
Highlands. 
In 1911 Dr. Campbell announced in the Geological Magazine that fossils had 
been found in the Highland border series north of Stonehaven, and, during this 
year, Dr. Jehu made a similar discovery in rocks belonging to this series near 
Aberfoyle. Papers on these subjects will be communicated to this Section. For 
my present purpose it will be sufficient to indicate the nature of the fossils and 
the lithological characters of the rocks containing them. 
The Highland border series north of Stonehaven and near Aberfoyle includes 
sheared igneous rocks, both lavaform and intrusive, with black shales, cherts, and 
jaspers. North of Stonehaven the fossils occur in thin, dark, flinty pyritous 
shale, while at Aberfoyle they have been found in shaly films at the edge of the 
chert bands. Several years ago radiolaria were detected in the cherts between 
Aberfoyle and Loch Lomond. From time to time these Highland border rocks 
have been carefully searched for fossils, but until recently with little success, 
owing to the intense movement to which they have been subjected, resulting in 
marked flaser structure in all except the most resistant bands. 
The fossils consist chiefly of horny, hingeless brachiopods, phyllocarid 
crustacea, worm tubes, and the jaws and chete of annelids. The genera of 
brachiopods comprise Lingulella, Obolus, Obolella, Acrotreta, and Linarssonia. 
The association of these brachiopods with phyllocarid crustaceans resembling 
Hymenocaris and Lingulocaris is suggestive of an Upper Cambrian horizon—an 
inference which is supported by the absence of graptolites. 
In the published Geological Survey maps these Highland border rocks are 
queried as of Lower Silurian age. This correlation was based partly on their 
resemblance to the Arenig volcanic rocks and radiolarian cherts of the Southern 
Uplands, and partly because, as shown by Mr. Barrow, they are overlain by an 
unconformable group of sediments, termed by him the Margie series. The 
cherts, the green schists, and the Margie series have shared in a common 
system of folding, and are unconformably surmounted by Downtonian strata 
near Stonehaven. Though the original correlation may not be strictly correct, 
it is probable, in my opinion, that representatives of both the Arenig and Upper 
Cambrian formations may occur in the Highland border series, and, further, 
that Upper Cambrian strata may yet be found in the Girvan area, as originally 
suggested by Professor Lapworth in correspondence with Dr. Horne. 
The Cambrian Fauna of North America. 
The classification of the Cambrian fauna found in North America is based 
on the researches of a band of distinguished paleontologists, comprising among 
the older investigators Billings, Hall, and Whitfield, and among modern workers 
Walcott, Ulrich, Schuchert, Brainerd, Seely, Ruedemann, Matthew, Clarke, and 
Grabau. Prominent among these investigators stands Dr. Walcott, alike for his 
original and exhaustive contributions to this branch of inquiry and for his com- 
plete mastery of the sequence and distribution of life in Cambrian time in North 
America. Indeed, geologists all over the world owe him a deep debt of gratitude 
for the services which he has rendered to Cambrian paleontology. 
Throughout the greater part of Cambrian time there existed in North 
America two distinct life provinces. The eastern one ran along the Atlantic 
coast from the north of Newfoundland to a point south of New York, extending 
only a short distance inland, with a faunal facies resembling that of North- 
West Europe, exclusive of the North-West Highlands of Scotland. The western 
province lay to the north-west of that just described, and ranged from Northern 
Newfoundland, south-westwards to Central North America and the Pacific 
Ocean. On the east side of the Rocky Mountains it swept northwards to British 
