ON THE OLDEST KNOWN FOSSIL^ ETC. 
345 
expected from the constantly recurring loss of 
some soluble matter in the waters wearing down 
the successively changed and upraised ma'sses^ 
and depositing their debris in consecutive sea- 
beds. The Canadian Surveyors also_, if not so 
early in finding fossils in metam.orphic rocks 
as Prof. W. B. Rogers^ who got Trilobites in 
the much- cleaved schists of Braintree (near 
Boston, U.S.), have found abundant evidences 
of primaeval life in still older rocks than those 
of Massachusetts. 
Sir W. E. Logan and his associates in the 
Geological Commission of Canada have had to 
occupy themselves with — 1st. The superficial 
shell-marls and peat-beds; glacial clays and 
sands with fossil shells, bones, &c. ; and glacial 
and gold-bearing drifts : 2nd. All the interme- 
diate Tertiary, Secondary, and Upper Primary 
formations, so well known elsewhere, being ab- 
sent, — the Lower Carboniferous conglomerates 
and sandstones of Bonaventure Island (2,700 ft. 
thick) : 3rd. The Devonian sandstones, shales, 
and limestones, with their bituminous beds and 
petroleum- springs, 6,000 ft. thick in the neigh- 
bouring States : 4th. The Upper Silurian Beds, 
about 600 ft. thick, containing gypsum and 
curious crystallites,"’^ or natural stony casts 
and moulds of crystals of sea-salt and sulphates 
of magnesia and soda, and yielding brine-springs 
in ISTew York : 5th. The Middle Silurian (about 
500 ft.) ; 6th. The Lower Silurian, in its many 
sub-divisions and complicated arrangement, 
about 7,000 ft. ; 6th. Coming up from beneath 
these, in places, are the quartzites, chlorite- 
schists, clay-slates, marbles, and bedded green- 
stone (altogether 18,000 ft. thick), which have 
been distinguished by Sir W. Logan as the 
Huronian formation : 7th. Still lower in the 
geological series, great and wide-spread rocks 
of Labrador-felspar and hypersthene, with 
gneiss and crystalline limestone, altogether 
10,000 ft. thick, have also been recognized by 
the Canadian geologists as constituting a strati- 
fied, though much-altered, formation (Upper 
Laurentian), resting unconformably ’’ on the 
worn edges of a still lower and older group of 
gneiss, quartzites, conglomerate, and marble. 
Fio. 1. Diagram showing the relations of the Laurentian and overlying Rock-systems in Canada. — 4. Devonian and Silurian; 3. Huronian; 2. Upper 
Laurentian; l. Lower Laurentian; a b the three zones of Lower Laurentian Limestones (c, the Grenville zone). * Granite. 
