Bibliographical Notice. 315 



variety, and rank. It may show itself in any country, in any part 

 of an epoch, or of a stage, in the middle or at the end of either, 

 being governed principally by the nature of the sediment." " Striking 

 examples of localization in time and place" are pointed out, as " the 

 rich Primordial beds of Western Newfoundland and of Quebec, the 

 crowded Pleta beds of Esthonia and Russia, the Trenton Limestone 

 of the State of New York, the Bohemian beds E. e. 1, 2, some of the 

 Welsh beds near the same horizon as those of Prague, the Lower 

 Helderberg rocks of New York;" and, on the other hand, isolated 

 localities and extensive areas nearly barren of life among the wide- 

 spread Silurian strata are indicated. He notes that out of 9030 spe- 

 cies of marine creatures registered as belonging to the Silurian pe- 

 riod, 4628 only are set down as met with in one locality of a certain 

 radius. Some species have inhabited many areas, as indicated by 

 their finding-places, from two to twenty-five ; such are the remain- 

 ing 4402. " Such a very great number of species (4628) being each 

 restricted to a single locality is an important fact. They are so 

 many specific centres." . . . ."It indicates that when species are com- 

 mon to two sets of beds, more or less apart, the connexion between 

 the latter is closer than has hitherto been thought, and, further, that 

 the absence of identical species in two beds does not forbid consider- 

 able relationship." . . . . " Multiple creation is implied, going on eveiy- 

 where, and affecting every form of life. The grand mystery of 

 creation has been in operation, all through the epoch, in thousands 

 of places." By a table showing the number of Silurian species, be- 

 longing to each of the orders, and known only at one place, we are 

 shown " that in each order the tendency of the species inhabiting only 

 one place is to one-half of the whole number," though some fall short 

 in the average and some are in excess. Other interesting facts, as 

 food for speculation, are also offered on this point. 2nd. First ap- 

 pearances (p. xxxvii). From observations resting wholly on natural- 

 history facts derived from the ' Thesaurus ' and similar sources, the 

 author regards the first appearance of a creature in its lowest trace- 

 able place in the succession of strata as being indicative of its time 

 and place of creation. This is liable to be mistaken sometimes, but 

 nearly sure to be ultimately corrected ; and he finds that, as a fact, 

 it may be reasoned from with tolerable safety. 3rd. The duration 

 of species (p. xxxviii). " This is an important part of vital statistics, 

 which, running up the whole scale of existences, reaches and deeply 

 interests man himself." Much has been written on this subject. 

 Dr. Bigsby points to M. Barrande's late researches as really showing 

 that " a species only exists in Bohemia during a part of a stage- 

 subdivision, and that the organic separation of part from part is very 

 sharp, leaving but a brief interval for the exercise of natural selection." 

 4th. Extinction and its causes (p. xxxix). 5th. Migration and con- 

 ditions favourable or inimical to distribution (p. xli). 6th. liecurrence, 

 or vertical range (p. xliv). 7th. Divergence (p. xlviii), or change of 

 residence from ground to ground. Under all these headings, the mu- 

 tual dependence of species, the influence of sea-bed, climate, depth, 

 feeding-grounds, and other physical conditions are important topics 



