The Fauna and Flora of the Silurian Period, 52o 



U8 to apply to one end of the earth information and reasoning gathered 

 at another.'' 



2. Locality. — Life is dependant upon local conditions and local 

 influences, which regulate its nature, condition, and almost absolute 

 quantity, — the resting place, the feeding ground, the home, are all 

 fixed by the concentration of conditions suitable to the well-being 

 and conservation of life, either from the plain to the mountain top, or 

 from tide mark to the most profound depths of the ocean. The 

 Thesaurus exhibits and enables us to reason upon the distribution, 

 and zone selected by species in hundreds of instances. In Silurian 

 times, as now, every large area of sea bottom had its own conditions, 

 its own fauna and flora; and we see, through the elaborate table 

 before us, that old disconnected areas are nevertheless, througb 

 generic, if not specific identity, connected by the common ties of the 

 great and predominant types of life ; that time and attendant circum- 

 stances allowed for distribution. The Thesaurus also declares to us, 

 through the analysis of its closely printed tabular columns, that the 

 physical state of land and sea was in Silurian times, as now, re- 

 stricted as to population, to those localities where the conditions were 

 most favourable for the maintenance and development of life ; and, 

 above all, we are enabled to arrive at conclusive evidence that the 

 maximum of life was, as now, usually local, i.e. adopting abundance, 

 variety, and rank as the test. In fact, localization in time and space, 

 a matter so essential to understanding the past distribution of organic 

 remains, can alone be wrought out by means of the facts and details 

 spread through the work before us. The author, at page xxxiv., in 

 speaking of the localization of life in time or space, as deduced from 

 his Thesaurus, says, "The rich Primordial beds of Western New- 

 foundland and of Quebec — the crowded Pleta beds of Esthonia and 

 Eussia — the Trenton Limestone of the State of New York — the 

 Bohemian beds E. e 1, 2 (=Upper Silurian : Third fauna. Lower 

 Limestone) — some of the Welsh beds near the same horizon as those 

 of Prague — the Lower Elderberg rocks of New York, are all striking 

 examples of localization in time and place." Again, " Parts of the 

 Middle Silurian of Wales and New York present a great dearth of 

 life, for well known reasons ; even the rich Silurian strata of Bohemia 

 are occasionally only so in the form of an oasis, the sediments around 

 them having scarcely a single tenant." 



The Potsdam sandstone (Primordial) of the St. Lawrence and 

 Mississippi valleys gives no signs of life for many thousands of square 

 miles except in patches, peopled chiefly with Lingnlce in incalculable 

 myriads. In these, amongst a host of other deposits, and localities, 

 the Thesaurus conspicuously shows and proves the doctrine of the 

 influence of locality on the nature and amount of life. So important 

 is the question of locality {i.e. definite localities) in connecnon with 

 the distribution of life, that we are obliged to look at some special 

 groups as having existed during Silurian times in this or that par- 

 ticular area only. Such is the case with the group of fishes, certain 

 genera of the Trilohita, and peculiar families of the Gasteropoda and 

 Gejphalojpoda. The Thesaurus, for example, catalogues sixty species 



