Revieics — Nicholsons Life- H ist ory of the Earth. 
223 
the other hand, we have presented to ns by our Continental brethren, 
as against tliis, such works as Pictet’s Traite de Paleontologie , 
d’Orbigny’s Cours Elementaire, Vogt’s Lehrbuch der Geologie und 
Petrefactenkunde, and, now publishing, Schimper and Zittel’s Hand- 
buch der Paläontologie. 
Prof. Nicholson’s “ Ancient Life-History ” is divided into two 
parts, “ The Principles of Palasontology,” 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 rocks 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 Eocks ” 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 tlieir 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 Palseontological 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 Palaeontological 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 tbe fossil state. 
“ Thus we arrive,” says Prof. Nicholson, “at the conviction that 
continuity 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.” 
