524 Reviews — Bigsbjs Thesaurus Siiuricus — 



contained in tlie 200 pages of seemingly unattractive matter, everj" 

 line of which however heli)S to build up a catalogue of past 

 existences and their history. The Thesaurus exhibits the complete 

 analysis of Silurian life in all its phases, and the highest generaliza- 

 tions and philosophical deductions may be drawn from the great table 

 itself. The fifty pages alone testify to the value of details, and how 

 much we are indebted to the patient labour of the author, who hopes 

 that the " more obvious facts and inferences to be derived from the 

 body of the work will invite a broader, more leisurely, and more able 

 study than is in his power to bestow." 



Amongst the more prominent questions arising from a close 

 analysis of the Thesaurus, the author has selected twelve ; three of 

 which are examples of the mode of analysis that the orders may be 

 subjected to, and the facts which may be deduced from them. 



The number of orders or groups adopted in the work are seven- 

 teen, but three only are selected in the introduction to show analysis, 

 viz., the Gasteropoda, Trilohita, and Echinodermata, these being evi- 

 dently chosen as showing greater diversity and detailed interest. 

 Nine other questions or enquiries are selected — two of them having 

 reference to the Primordial stage and the Bohemian area, whilst 

 seven embrace questions of the highest importance to a right and 

 philosophical understanding of the distribution and laws of life 

 through all time. 



1. Universality ; — is here used in a physical as well as natural 

 history sense. The former refers to the once universal distribution 

 of the Silurian seas, (and, as a consequence, of Silurian rocks,) 

 more or less over the globe ; and, secondly, the universality of the 

 distribution of numerous genera and species in and through one or 

 other of the three stages comprising the Silurian system. 



Examples occur through the Thesaurus of many species of Mol- 

 lusca occurring in twenty -five difi'erent countries, extensive and far 

 apart, a proof of the amount of time required for their distribution 

 and migration in space ; other genera, on the other hand, lived on 

 during the deposition of a whole group of rocks, thus illustrating 

 their duration in time. In this way we know of the range of Theca 

 triangularis through all the many different sediments comprising the 

 Hudson Eiver group in North America, and that it is also a common 

 British Pteropod in the Caradoc rocks of Ireland, Denbighshire, 

 Westmoreland, Spain, etc. The Thesaurus shows us that 210 species 

 of all orders are common to Europe and America ; sixty European 

 Silurian genera are common also to South Australia; and eighteen 

 species of the Graptolites of Australia are also common to, and 

 identical with, those of North America and Europe- 



Som#Silurian fossils may be said to be cosmopolitan. The The- 

 saurus exhibits this on almost every page. After tersely noticing 

 many facts connected with, and as proof of this universality of the 

 Silurian epoch, Dr. Bigsby sums up this commencement of the 

 universality of epochs by stating that "it is a great fact and enables 



^ These are — 1. Universality. 2. Locality. 3. First appearance. 4. Duration, 

 longevity, and extinction. 5. Migration. 6. Eecurrence. 7. Divergence. 



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