448 TRANSACTIONS OF SECTION C. 
Section C.—GHOLOGY. 
PRESIDENT OF THE SEcTION.—B. N. Peacn, LL.D., F.R.S. 
THURSDAY, SEPTEMBER 5. 
The President delivered the following Address :— 
Tus RELATION BETWEEN THE CAMBRIAN FAUNAS OF SCOTLAND AND 
Nortu AMERICA. 
CONTENTS. 
PAGE 
I. Introduction S : : : ; : ‘ : : : . 448 
Il. The Cambrian Fauna of Scotland . : : : ; : : . 449 
It. The Cambrian Fauna of North America , . 453 
IV. Cambrian Paleogeography between North America and North-West Europe . 456 
Introduction. 
Ever since the announcement made by Salter in 1859 that the biological affini- 
ties of the fossils found in the Durness Limestone are more closely linked with 
American than with European forms, the relation between the older palzozoic 
faunas of Scotland and North America has been a subject of special interest to 
geologists. The subsequent discovery of the Olenellus fauna in the North-West 
Highlands furnished striking confirmation of Salter’s opinion. This intimate 
relationship raises questions of prime importance bearing upon the sequence and 
distribution of life in Cambrian time in North America and North-West Europe, 
on the probable migration of forms from one life-province to another, and on 
the paleogeographical conditions which doubtless affected these migrations. 
On this occasion, when the British Association revisits the border of the 
Scottish Highlands, it seems appropriate to refer to some of these problems. 
With this object in view I shall try to recapitulate briefly the leading features 
of the life history of Cambrian time in Scotland and North America, to indicate 
the relation which these life-provinces bear to each other, and, from these data, 
to draw some inferences regarding the probable distribution of land and sea 
which then obtained in those regions. 
The two great rock groups in Scotland that are universally admitted to be 
older than Cambrian time are the Lewisian Gneiss and the Torridon Sandstone. 
The Lewisian Gneiss, as mapped by the Geological Survey, consists mainly of 
igneous rocks, or of gneisses and schists of igneous origin. But, in addition to 
these materials, we find, in the Loch Maree region, schists of sedimentary origin, 
comprising siliceous schist, mica-schist, graphite-schist, limestone, chert, and 
other sediments. The association of graphite-schist with limestone and chert 
suggests that we are here deaiing with rocks that were formed at or near the 
extreme limit of sedimentation, where the graphite, the limestone, and the chert 
were probably accumulated from the remains of plankton. But this assemblage 
has been so completely altered into crystalline schists that all traces cf original 
organic structure in them have been destroyed. 
