﻿JRevieics — Nicholsons Life-History of the Earth. 223 



the other hand, we have presented to us by our Contmental brethren, 

 as against this, such works as Pictet's Traite de Paleontologie, 

 d'Orbigny's Cours Elementaire, Yogt's Lelirbuch der Geologie und 

 Fetrefactenhunde, and, now publishing, Schimper and Zittel's Hand- 

 huch der Palieontologie. 



Prof. Nicholson's "Ancient Life- History " is divided into two 

 parts, "The Principles of Palaeontology," and " Historical Palaeon- 

 tology." In the first the science is defined, the nature of fossils and 

 process of fossilization described, the origin and mode of formation 

 of sedimentary rooks discussed, and brief descriptions given of the 

 chief kinds of the latter, illustrated by vignettes of microscopic 

 sections of the rocks described. In the " Chronological Succession 

 of the Fossiliferous Rocks " the student is taught the use of fossils, 

 the assistance rendered by them in the sub-division and working out 

 of the historical succession of the sedimentary formations, and due 

 attention is paid that the student shall have a clear conception 

 of the deductions to be drawn from an examination of any set of 

 fossils, as to their age, origin, whether the deposit was accumulated 

 under fluviatile, lacustrine, or marine conditions, and whether repre- 

 senting a littoral, deep-sea, or actual shore deposit. The evidence 

 afforded by fossils as to climate is also dwelt on, but it is judiciously 

 pointed out that all conclusions under this head, based as they 

 are upon the present distribution of animal and vegetable life on 

 the globe, must be accepted with caution, and may be, to a certain 

 degree at least, vitiated or modified by certain well-established facts, 

 such, for instance, as the occurrence of groups so unlike anything 

 now existing that no theory as to the climate under which they 

 existed can be drawn from them, neither is it certain that the habits 

 and requirements of extinct animals were similar to their represen- 

 tatives of the present day. In the chapter devoted to " Breaks 

 in the Geological and Palaeontological Record," the contemporaneity 

 of groups of strata is touched on, and it is pointed out by Prof. 

 Nicholson that this may hold good for strata containing identical, 

 fossils within the limits of a single geographical region ; but when 

 the distance between the areas where the strata occur is greatly 

 increased, the case is different, and is accounted for by a migration of 

 the fauna, rather than that they were contemporaneous in the strictly 

 literal sense of the term. The Geological and Pal^ontological records 

 are considered to be sufficiently extensive to throw the balance of 

 evidence in favour of the " continuity theory," as opposed to that 

 of intermittent and occasional action in the production of life from 

 the Laurentian upwards to the present day. The interruptions and 

 breaks in the records are accounted for by the occurrence of an 

 unconformability between any two sets of strata, supplemented by 

 metamorphism, and supported by the absence of an appreciable 

 number of animals, of which no trace is found in the fossil state. 

 "Thus we arrive," says Prof. Nicholson, "at the conviction that 

 continuitij is the fundamental law of geology, as it is of the other 

 sciences, and that the lines of demarcation between the great forma- 

 tions are but gaps in our own knowledge." 



