REVIEWS. 
89 
that, ))y .1 full and generous acknowlcilgnient of the well-known and valuable ser- 
vices it{ tlic late Rev. T. T. Lewis, of Ayniesliury, the autiior of " Siluria" has'imt 
one oft-spoken i)oint out of the reach of his detractors. 
" Ce n'est pas avec des microscopes," says J)e Saussure, " qn'il faut observer \es 
niontiignes ; and it is not by local or limited observation alone that a grand 
system like the "Silurian," as it now stands, could have been worketl out. 
Sir Roderick is as essentially a general in .science as a Napoleon or Wellington 
was of troops ; and he coidd afford to give away every title to originality of detnil, 
and yet stand a pre-eminently great man. lie would even thus have accomplished 
a generalization and gronpin,^ of a character so extended as to have been totally 
out of the reach of mere local workers, had they even possessed the talents of a 
Barrande. 
Sir Roderick has, however, been not only a successful generalizer. but also a 
close and keen inspector of facts, as his recent investigations ana deductions 
regarding the crystalline strata of the north-western Highlands of Scotland and 
very many other instances would show ; and hence his capability of judging of the 
value of those other labourers in the field of the earth's ancient liistory who have 
put the stores of their accunudations at his command. 
We now pass to what the author of " Siluria " has done since the previous 
issue of his work. This is, indeed, briefly told in tlie preface to the book itself, 
and nuich of the most recently acquired matter is embodied m the introductory 
chajiter. 
In the first jilace, there is the most important section, exhibiting the lowest 
rocks in the British Isles as lying beneath all the oldest sedimentary and fossilife- 
rons rocks previously known, described in the ojiening pages and illustrated by 
the delicate coloured frontispiece of the " hoary mountains " bounding Loch Assynt 
westward from Inchnadamft. 
The oldest gneiss of Scotland, parti ■ularly on the west side of Sutherland and 
Ross, is unconformably surmounted by mountain-masses of conglomerate and sand- 
stone, formerly considered as Old Red Sandstone, but now demonstrated to be of 
Cambrian age, from the fact of their being overlaid by quartz-rock and crystalline 
limestone, enclosing at Durness masses of unaltered rock, in wliich Mr. C. Peach, 
of Wick, has discovered Silurian fossils of the age of the lowest portion of the 
Llandeilo beds. 
The identification of the Bala rocks and fossils with those of the Caradoc for- 
mation, and the determination of a passage-zone of rocks at Llandovery, connecting 
the Lower and Upper Silurian strata, are also new features. 
The classification of the Devonian or Old Red Sandstone Formation has been 
improved, the Cephalaspis and Pteraspis zone Ijeing demonstrated to be the real 
base of this group, passing regidarly and gradually downwards into the ui)permost 
Silurian rock. Hence the Caithness flags and their extension into Ross an(l Moray 
are no longer to be 'considered as equivalents in age to that zone, but are referable 
to a middle zone or period. 
During a personal e.xcursion last summer, Sir Roderick reassured himself that 
flagstones, such as tliose of Caithness, and containing similar fishes and plants, 
rejiosed near Kirkwall, in the Orkneys, upon a lower red sandstone, and are sur- 
mounted in several of the islands by another sandstone of a light yellowish colour. 
In Moray, in the presumed equivalent of this yellow series which there passes up 
into a fine wliite sandstone, during the past year, most important discoveries of 
fossil reptilian remains have l)een made ; Mr. Patrick Duft' and others, of Elgin, 
having obtained casts and liones of the Sluyonolepis Robert snni (of Agassiz), from 
which Professor Huxley has been enabled to establish the reptilian nature of tliis 
creature formerly supposed to be a fish. 
Adilitional and more highly instinctive specimens of foot-tracks from the Cum- 
mingstone quanies between Burgh Head and Lossie Mouth, — first made known 
through the wi-itings and labours of Ca])tain Brickenden and Mr. Patrick Duff, — ■ 
have shed additional light by the establishment of their relations to that extra- 
ordinary creatm-e, the organization of which ranks so high as to cause many excel- 
lent geologists to suspect whether the strata in which its osseous remains, and its 
imprints, have been found, may not be possibly of Permian or Oolitic age ; but on 
