488 
SILTJKIA. 
[Chap. XX. 
traced life downwards in the successive crusts of the earth, to the same 
* Primordial ' Silurian zone as their cotemporaries have done in Britain*, 
Scandinavia, and Bohemia. The American geologists have evidences, in 
their lowest Silurian (Potsdam) beds, of numerous trails of animals, pro- 
bably Crustaceans, by which a film of mud or sand formed by one tide was 
tracked and burrowed before another covered the impressions, and left 
them to future ages as proofs of layers deposited on the shores of former 
lands. Again, in other Silurian beds of the far West, there exists the same 
abundance of Coral-reefs as in Britain, and the still stronger evidence of 
pebbly and sandy shores which never contain the trace of a Land Plant. 
"Why, therefore, wander from such plain facts into theory ? And why not 
admit (what is, indeed, in accordance with all we have observed) that 
nearly all the Silurian era had passed away before Trees grew upon the 
land or Fishes swam in the waters? The Silurian rocks extend over 
areas as large as, if not larger than, any great systems of the following 
periods; and yet in them alone of the whole geological series is there, 
I repeat, an entire absence of an arborescent vegetation derived from the 
then adjacent lands. 
Here it is well to remind the student of the wide, if not universal, 
spread of the primeval strata (including many igneous rocks which were 
associated with them). We may suppose that when such extensive 
Palaeozoic sea-bottoms were raised into lands the former continents, from 
which the sediments had been derived, were submerged and disappeared. 
Be this as it may, we know that in all quarters of the globe Silurian 
or older strata constantly lie in juxtaposition to the other overlying 
Palaeozoic formations ; and hence it is impossible to apply to the lower 
strata any reasoning which does not also refer to those which repose upon 
them ; for, as the Silurian rocks are constantly found in the same lati- 
tudes as the Devonian and Carboniferous, why is it that in enormous 
masses of the one there are never found traces of Yertebrata and Land 
Plants, and that in the very same region remains of both these classes 
abound in the other? By no theoretical suggestion, therefore, can the 
fair inference be evaded that things which did not exist during the Lau- 
rentian, Cambrian, and Silurian periods appeared in the same zones of the 
earth during the following ages. 
The Uniformitarian, who would explain every natural event in the 
earliest periods by reference to the existing conditions of being, is thus 
stopped at the foundation-stones of the great natural edifice, each story of 
which has been inhabited by different creatures. Nature herself, in short, 
speaks to him through her ancient monuments, and tells him that, though 
she has worked during all ages on the same general principles of destruc- 
* Mr. Salter lias described a trail of Hymeno- vey) : see Quarterly Journal of the Geological 
aris vermicauda, in the Lingula-flags of North Society (May 1854), vol. x. p. 208. Other tracks 
Wales (' Lowest Silurian ' of the Geological Sur- also are common in these beds. 
