80 Reviews — MurcMson^s " Siluria." 



Survey of Canada have laboriously mapped and, as it were, unravelled 

 (besides tlic many thousand feet of Lower Carboniferous, Devonian, 

 and Silurian strata of that country) — a great lower series of quart- 

 zites, chloritic schists, clay-slates, marble, and bedded diorites, alto- 

 gether 18,000 feet thick, and called by them ''Huronian" (probably 

 equivalent to our ''Cambrian" rocks) ; and inferior still to this, they 

 recognised the great "Laurentian System," Upper and Lower. 

 The upper portion consists of the wide and crumpled sheets of hyper- 

 sthene and dark felspathic rock so characteristic of Labrador, with 

 gneiss and imbedded marble, altogether 10,000 feet thick ; and this, 

 as a really stratified though metamorphosed formation, "rests un- 

 conformably on the worn edges of a still older group of gneiss, 

 quartzites, conglomerate, and marble, 20,000 feet thick at least, 

 crumpled and crystalline, converted here and there into granite, and 

 traversed by intrusive syenites and greenstones." These Lower 

 Laurentian rocks are not only the disguised sands, clays, shingle, 

 and calcareous sea-beds of the primgeval earth, but bear witness to 

 the life of the period ; for their seams of Graphite represent coal or 

 other carbonaceous layers of animal or of vegetable origin, — their 

 apatite, fluor, iron-oxide, and pyrites ''have reference probably to 

 former animal organisms and their decompositions," — worm-tubes 

 occur in the schists, — and, besides obscure fragments like those of 

 crinoids, corals, and shells, the structure of a real Foraminifer has 

 been detected by Logan and Dawson in these old Laurentian lime- 

 stones. Similar in relative position and in structure to that of 

 Canada, the gneiss of Cape Wrath and the Lewis belongs to Sir 

 William Logan's well-established "Laurentian System;" and, grace- 

 fully acknowledging his friend's hard-won discovery of this the 

 earliest stage of the earth's terraqueous history. Sir Eoderick thus 

 dedicates this new edition of his work — "To the geologist who has 

 not only applied my (Silurian) classification to the vast regions of 

 British North America, but has taught us by his recent important 

 researches that the Laurentian Eocks constitute the foundation-stones 

 of all Palgeozoic deposits in the crust of the globe, wherever their 

 foundations are known." 



The condition of these old schists and gneiss in Bavaria and 

 Bohemia are carefully treated of, and indications of their existence 

 in Norway, Spitzbergen, Finland, and elsewhere are given in 

 " Siluria." 



The nature, structure, and special features of the Cambrian rocks 

 of the Longmynd, 26,000 feet thick, of Harlech and Llanberris, of 

 Anglesea (where they are metamorphosed), of the North- Western 

 Highlands, of Norway, Bohemia, and elsewhere, are next fully 

 described and freely illustrated. These were once the Bottom-rocks, 

 — these were once "Azoic;" but now the disentanglement of the 

 so-called systems of mica-schist, slate, and gneiss, has opened out 

 the above-mentioned 30,000 feet of still lower stratified formations 

 (Laurentian) ; and the discovery of fucoids, worm-burrows, the 

 Oldhamia, a Lingula, and a Trilobite, has partially, at least, educed 

 the fauna and flora of these old Cambrian times. 



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