82 Reviews — Nicholson and Lydekker's Palaeontology. 



treated. There is no doubt, however, that the work furnishes the 

 student with an excellent summary of the leading principles and 

 facts of palaeontological science — by far the most complete which 

 has ever been published in the English language — and any one who 

 wishes to gain either a general knowledge of the past life of the 

 earth, or a guiding key to any particular division, cannot do better 

 than make use of its assistance. 



The first volume, for which Professor Nicholson is specially 

 responsible, contains the General Introduction and the Invertebrata. 

 It comprises 44 chapters, of which seven are devoted to the Intro- 

 duction. The first part of this relates to the character and mode of 

 formation of the sedimentary rocks, and the conditions under which 

 fossils occur in them. Good figures are given of the microscopic 

 structure of different varieties of fossiliferous limestones, including 

 the White Chalk, which is compared with a section of the Globi- 

 gerina mud from the depths of the Atlantic. Keference is also made 

 to the organic siliceous rocks, such as flint and chert, which, as we 

 now know, owe their origin to Sponges principally. Following 

 a table of the chronological succession 'of aqueous rocks, full 

 explanations are given of the migration of species, contemporaneity 

 and homotaxis, the value to be attached to marine, as compared with 

 land and fresh-water fossils; geological continuity, lite-zones, and 

 the now obsolete doctrine of intercalated colonies In the succeeding 

 chapter the causes of the imperfections of the Palaeontological 

 Record are pointed out, and some remarks made on the theory 

 propounded by Murray and Renard that there are no geological 

 representatives of abyssal deposits. It is evident, however, that 

 certain portions of the sedimentary series fully correspond with the 

 Foraminiferal ooze, the Eadiolarian ooze, the Diatom ooze, and even 

 with the Pteropod ooze, and it is by no means improbable that some 

 of the variegated, fine-grained muds of the Cambrian and Ordovician 

 strata may correspond to the abyssal clays of the present oceans. 

 The question of the climatic conditions of the earth in former 

 geological periods is also one on which no certain conclusions can 

 be drawn from fossils — at all events on those from the older rocks ; 

 but the researches of Neumayr on the animal life of the Jurassic 

 period indicate the existence at that epoch of climatic zones similar 

 to those of the present day, and there is also a certain amount of 

 evidence of the recurrence of Glacial periods at different epochs in 

 the past. 



As regards the terms used in palaeontology, the author remarks 

 that they are the same as those employed by the zoologist ; but 

 owing to the fact that as almost without exception the specific 

 characters of fossils must necessarily be founded on the hard structures 

 only, and these often imperfectly preserved, it follows that a palaeon- 

 tological species cannot be expected to have the same value as that 

 which a zoological species ought to have when the entire structure 

 of the organism can be taken into account, and consequently both 

 the species and the genus must be accepted in a wider and less strict 

 sense in palaeontology than in zoology. The author adopts the 



