The Fauna and Flora of the Silurian Period, 



hranchiata-Monomijana, 1 only out of 1635 ; Dmyaria none out of 

 526 ; Gasteropoda 1 only out of 944. 



We select the following table out of many in the introduction to 

 show the mode of generalization. All the twenty- six tables are 

 constructed from the body of the Thesaurus ; — Dr. Bigsby re- 

 marks, a Montreal fossil we trace Southwards to Pennsylvania, 

 Westwards into Minnesota, and Eastwards to Anticosti ; and Minne- 

 sotans are found in the Texas, etc., and the Australian Diplograpsus 

 pristis (Hisinger) also flourished in Britain, and Canada on the same 

 zone. The same species of Trilobites, Corals, and Brachiopods are 

 found along lines of coast 6000 miles long, Iraceable from Canada 

 to Kussia, Britain, etc. 



Directions. 



1 



O 

 § 



ft 



M 

 O 



a 

 < 



s 



o 

 c 



1 



i 

 1 



c3 



1 



i 



1 





.3 

 I 



a 

 S 



-a 





 p. 







£ 



1 



rt 

 





 1 



i 



5 



►4 

 ■< 



Eh 

 



From Europe to Ainerica(W) 



From America to 'Europe (E) 



2 



217 

 11 4 



z 



2 

 2 



8 

 1 



24 



'3 

 1 



4 



1 



30 

 31 



6 

 14 

 52 



72 



i 



6 



*8 

 8 



4 



2 



10 



16 



"1 



7 

 8 



3 

 3 

 9 



15 



— 



— 



35 



30 



145 



210' 



The Isozonals in both hemispheres 

 Total 



1 

 3 



2 

 5 



17 



6. Becurrenee of vertical range. — The author of the Thesaurus 

 devotes much space to the discussion and elucidation of principles 

 in this highly important question in stratigraphical Geology. The 

 value of the whole Thesaurus, its well-stored columns and facts, is 

 apparent when we come to the question of the recurrence of species 

 in time ; their upward passage and life through long ages and succes- 

 sive generations. The task of searching whole libraries for such 

 details (which otherwise must have been done by the student) are 

 avoided if we consult the Thesaurus with fidelity ; and whether we 

 hold the views of those who believe in the limited duration of species 

 in time or not, the facts as they occur all through the Thesaurus will 

 stand the same. We are enabled to trace the range of any given 

 species through the different stages, and may, we think, modify the 

 notion possessed by some Palaeontologist as to the distinctness of 

 species found in different horizons; for progress daily teaches us 

 that we must not too strictly narrow the stratigraphical limits of 

 species, neither would we, on the other hand, advocate destroying 

 all sharp lines of demarcation ; both views have their value, when 

 our diagnoses are not too forced or narrow. Denudation and breaks 

 in time must have their weight even here. " Species," says the 

 author of the Thesaurus, "are the principal time-tests, genera and 

 families run through so many stages and epochs that they characterise 

 none." The opposite is the case, however, with species well deter- 

 mined, — they are the only tests of age and succession, and in great 

 overlaps and some apparently superposed strata, species only will 

 determine the conditions. The author of the Thesaurus has con- 

 structed out of his work a very important synoptical view of Silurian 



