Reviews — MiirchisorCs " Siluria." 87 



in Australia, Whitney in California, and David Forbes in South 

 America, are especially referred to ; and the following are the con- 

 clusions arrived at: — " 1. That looking to the world at large, the 

 auriferous veinstones in the Lower Silurian Eocks contain the greatest 

 quantity of gold. 2. That where certain igneous eruptions pene- 

 trated the Secondary deposits, the latter have been rendered auriferous 

 for a limited distance only beyond the junction of the two rocks. 

 3. That the general axiom before insisted upon remains, that all 

 Secondary and Tertiary deposits, except the auriferous detritus in the 

 latter not so specially affected, never contain gold. 4. Tliat as no 

 unaltered purely aqueous sediment ever contains gold, the argument 

 in favour of the igneous origin of that metal is prodigiously strength- 

 ened ; or, in other words, that the granites and diorites have been 

 the chief gold-producers, and that the auriferous quartz -bands in the 

 Palaeozoic Rocks are also the result of heat and chemical agency." 



In the last chapter of his work, Sir Roderick, taking a general 

 view of ancient life from its earliest traces, points out the progress 

 of creation after a long Invertebrate Period (represented by the 

 Laurentian, Cambrian, Lower, Middle, and part of the Upper 

 Silurian deposits) to the first period of Fishes (in the Lower 

 Ludlow series), followed by the earliest epochs of Reptiles (Am- 

 phibia in the Coal and Lacertilia in the Permian) and of Mammals 

 (in the Rhaetic beds) ; thus indicating a succession of life from lower 

 to higher classes, until Man crowns the scale of beings. Another 

 subject which our author here keeps before his readers is, that in 

 primaeval times there must have been a far greater intensity of 

 action in the cracking, crushing, crumpling, and altering of the 

 materials of the earth's crust, — that the concomitant earthquakes and 

 volcanos were more energetic, and productive of greater special 

 results, — that storms and floods, torrents and waves, were all more 

 violent and more incessant in action, — that the degradation and re- 

 arrangement of earthy and stony matters went on more ceaselessly 

 and with greater results, both in the destruction and in the deposition 

 of strata, — and that these last were more readily buried, more quickly 

 changed, and more suddenly brought up by lateral squeeze and up- 

 ward thrust than is now the case with sea-beds, volcanos, and moun- 

 tain-chains. The great former changes of the surface, the enormous 

 dislocations and wide and perfect denudations, the great fractures 

 and reversals of strata, are brought forward as the results of great 

 movements of the crust, and inexplicable by reference to modern 

 causations, such as the faint shrinkings, the limited volcanos, the 

 transient showers, the weak rivers of to-day. That the working 

 giant, Ice, did not exist in those old days our author fully believes ; 

 for the glaciers would require mountains, and those were not, if the 

 uniformity of the old deposits, the world-wide distribution of 

 similar animals, and the necessarily equable temperature, are fully 

 allowed for. It is well now-a-days for thoughtful beginners to look 

 on both sides of the many geological questions they meet with ; and 

 here are the real " conservative " opinions of an old geologist, not 

 lagging behind, but well up in the march of progress, — keeping in 



