xxxiv FACTS AND OBSERVATIONS. 



It is in the Arctic seas of America, South-eastern Hudson's Bay, Sardinia, Spain, and such like 

 imperfectly known countries that certain important stages are said to be wanting "*. But the visible 

 geographic spread of these strata is often very great. So extensive are the easily traceable Silurian 

 areas of North America (2000 miles across) and the more disturbed and fractional areas of Western 

 Europe (1200 miles across ?), that it only needs a short and easy step in advance to induce a belief 

 in a former universal prevalence and external domination of this system. 



Sufficient territory resting on Silurian rocks has been spared from oscillatory action to enable 

 us to trace it, in one or other of its parts, over a large part of the earth. We follow it, with 

 many a bend and gap, from England, through France or Spain, into Germany, Turkey, Russia, and 

 so on, to India and Australia. Or we arrive in North America, the interspaces being filled up 

 either by sea, by newer rocks, or by kindred Palaeozoic rocks, which themselves irresistibly bespeak 

 our strata near at hand. Here, as well as in South America, this period is in abundant display. 

 More than fifty great terrestrial spaces, scattered over the whole earth, are occupied with some por- 

 tion of the Silurian succession of rocks, with their proper stratigraphical habitudes, connexions, &c. 



This is only a very small fragment of the argument in favour of the universality of epochs as 

 defined above. It is a great fact, and it enables us to apply to one end of the earth information 

 and reasoning gathered at another. 



LOCALITY. The ' Thesaurus ' brings conspicuously into view the great influence of locality on 

 the nature and amount of life. 



It is a power, in the strongest sense of the word, universal and great ; or rather we ought to say 

 that it operates by a concentration of powers peculiar to itself. We shall see in some thousands of 

 instances that localities had exclusive privileges in regard to life, as far as we now know. 



In every considerable region the collector finds much that is new and peculiar, the union with 

 other Silurian districts being often mainly generic. And it is so at the present day. Every tolerably 

 large space of sea-bottom has its own conditions and its own fauna. The exact nature of that sea- 

 bottom cannot be safely predicated ; for it is only to be learnt by actual examination. The physical 

 state of land and sea was and is as local as the population ; for it is produced by plutonic and other 

 agencies, all limited in space. So the dwellers among these local changes must be local too, and 

 subject to removal at any moment. Thus, if we suppose a rocky islet to be placed to-day in the 

 sea, then immediately a new set of actions begin to operate upon materials around, organic and 

 inorganic. Most of the old things and conditions disappear. New shore-lines, new currents, new 

 depths, and new life appear. The first occupants of any portion of the globe who shall point out ? 



The maximum of life is usually local, meaning, by that expression, the largest combination of 

 abundance, 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. 



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, are all striking examples of localization in time and place. 



Parts of the Middle Silurian of Wales and New York present great dearth of life, and for a 

 well-known reason. Even the rich Silurian strata of Bohemia are occasionally only so in the form of 

 oases, the sediments around them having scarcely a single tenant. The Potsdam sandstone of the 

 St. Lawrence and Mississippi valleys gives no signs of life for many thousand square miles, except 

 in patches, peopled chiefly with Lingulse in incalculable myriads. 



North-east Central America (the United States and the Canadas) has probably received in an 

 equal degree with Europe the attention of the palaeontologist ; but the latter, up to the year 1866, 



* Dr. Hayes is said to have met with a patch of Lower Silurian in the Arctic seas. 



