566 Revieus — R. Etheridge^ s Manual of Geology. 



is premature, if not altogether objectionable. Nevertheless it is a 

 rough and ready sort of waj'^ of separating the several series, and 

 certainly it is impossible not to admit the distinctness of such a 

 fauna as the Arenig for instance, ushered in by an influx of Grapto- 

 lites, and terminated, Mr. Etheridge tells us, by a change of genera 

 and species which has scarcely any parallel in the Paleeozoic rocks. 



That this should be the case in the Lake District is not to be 

 wondered at, since some of the thickest volcanic accumulations 

 known in these islands are superimposed ; and the author hints 

 (p. 68) that the Borrowdale series may, in Wales, be represented 

 by the Aran and the Arenig volcanic beds, the Llandeilo slates, 

 and the Snowdon volcanic series. Subsequently (p. 80) he throws 

 doubts on the Llandeilo age of the Borrowdale rocks "from the 

 fact that the great series of Llandeilo rocks in the south-west of 

 Scotland appears to be free from intermixture with contemporaneous 

 igneous matter." 



The Llandeilo age of the Lower Moffat Shales is determined 

 through the total absence of those complex Arenig forms of Diclio- 

 grapti, Tetragrapti and Pliyllograpti, so characteristic a feature of 

 the Graptolithic fauna of the Skiddaw, Shelve, and St. Davids 

 beds, together with their Canadian equivalents. It is through the 

 Hydrozoa, Crustacea, and Brachiopoda chiefly that the Llandeilo 

 rocks are connected with the overlying Bala or Caradoc ; 77 species 

 out of 175 passing from the former to the latter. The Sedgwickian, 

 we know, would do away with the Llandeilo altogether as a geolo- 

 gical series, and Mr. Etheridge considers that the large community 

 of species is confirmatory of the views of Sedgwick : yet in spite of 

 this he gives great prominence throughout to the " Llandeilo Series." 

 On the other hand, no more than 102 species out of 610 pass from 

 the Caradoc to the Lower Llandovery, which, together with the 

 Upper Llandovei'y, he suggests might be classed as passage-beds 

 under the title of Middle Silurian. Under this arrangement the 

 Wenlock and Ludlow series would constitute the fourth and final 

 section of the Lower Palaeozoic rocks. 



It is hardly necessary to remark that in all cases the foreign 

 equivalents of each group or series are discussed at some length ; 

 and if the reader requires further information, he has only to consult 

 the works to which reference is made. Meantime he is reminded of 

 the immense amount of research which has been effected of late 

 years in the Lower Paleeozoic areas both of Europe and America. 



On pp. 139-141 is given a " Tabular view of the Cambrian and 

 Silurian strata, with Physical and Palseontological particulars." In 

 this table the Menevian series is altogether omitted, or else absorbed 

 in the Lingnla Flags. On pp. 142-149, Table XVI. the author 

 enumerates the "Organic remains of the Lower Paleeozoic Strata" : 

 the genera are arranged alphabetically, whilst the number of species 

 is brought down to date. Finally, on p. 150, Table XVII. shows 

 the numerical history of the " Lower Palgeozoic Series." 



We have noticed at some length the author's treatment of the 

 Lower Pala30zoic rocks, both because he is known to be especially 



