REVIEWS. 



89 



that, by a full and generous acknowledgment of the well-known and valuable ser- 

 vices of the late Rev. T. T. Lewis, of Aymesbury, the author of " Siluria" has*put 

 one oft-spoken point out of the reach of his detractors. 



" Ce n'est pas avec des microscopes," says De Saussure, " qu'il faut observer les 

 montagnes ;" and it is not by local or limited observation alone that a grand 

 system like the " Silurian^" as it now stands, could have been worked out. 

 ^ir Roderick is as essentially a general in science as a Napoleon or Wellington 

 was of troops ; and he could afford to give away every title to originality of detail, 

 and yet stand a pre-eminently great man. He would even thus have accomplished 

 a geiierahzation and grouping 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 

 1 Barrande. 



! Sir Roderick has, however, been not only a successful generalizer, but also a 

 i close and keen inspector of facts, as his recent investigations and deductions 

 j 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 history who have 

 ; put the stores of their accumulations at his command. 



J We now pass to what the author of " Siluria " has done since the previous 

 issue of his work. This is, indeed, briefly told in the preface to the book itself, 



I and much of the most recently acquired matter is embodied in the introductory 

 chapter. 



In the first place, there is the most important section, exhibiting the lowest 

 rocks in the British Isles as lying beneath all the oldest sedimentary and fossilife- 

 rous rocks previously known, described in the opening pages and illustrated by 

 the delicate coloured frontispiece of the " hoary mountains " bounding Loch Assynt 

 westward from Inchnadamft". 



The oldest gneiss of Scotland, particularly on the west side of Sutherland and 

 Ross, is un conformably surmounted by mountain-masses of conglomerate and sand- 

 stone, formerly considered as Old Red Sandstone, but now demonstrated to be of 

 Cambrian age, fi'om the fact of their being overlaid by quartz-rock and crystalline 

 limestone, enclosing at Durness masses of unaltered rock, in which 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 Oephalaspis and Pteraspis zone being demonstrated to be the real 

 base of this group, passing regularly and gradually downwards into the uppermost 

 Sihirian rock. Hence the Caithness flags and their extension into Ross and 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 excursion last summer, Sir Roderick reassured himself that 

 flagstones, such as those of Caithness, and containing similar fishes and plants, 

 reposed 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 white sandstone, during the past year, most important discoveries of 

 fossil reptilian remains have been made ; Mr. Patrick Duff' and others, of Elgin, 

 having obtained casts and bones of the Stagonolepis Robertsoni (of Agassiz), from 

 which Professor Huxley has been enabled to establish the reptilian nature of this 

 creature formerly supposed to be a fish. 



Additional and more highly instinctive specimens of foot-tracks from the Cum- 

 mingstone quarries between Burgh Head and Lossie Mouth,^ — first made known 

 ■through the writings and labours of Captain Brickenden and Mr. Patrick Dutf,— 

 have shed additional hght by the establishment of their relations to that extra- 

 ordinary creature, 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 



