822 Siluria—Present State of Geology. 
no evidence whatever in any former geological period! On the 
contrary, whilst eyery boulder of the primary, secondary, or older 
tertiary rocks bears on its surface the signs of having been winter- 
worn, or rounded by aqueous or atmospheric agency; the great 
blocks of the later cold period, (gigantic in comparison with all that 
preceded them), are often angular, or nearly in that state in which 
they left the mountain side, before, in short, they were wafted over 
seas or lakes, to be dropped, at remote distances from their parent 
rocks, upon sediments which, by subsequent elevation, have been 
made portions of our continents. Hence, independently of the in- 
dications of a more equally diffused and warmer temperature in 
olden times than at the present day, these large erratics are in them- 
selves decisive testimonials of that intense cold which, it is believed, 
was principally due to the great, elevated masses of land, which 
specially characterize the modern period. 
“ Receding backwards from this general phenomenon, which, con- 
tinuing into our own times, has been so skilfully illustrated by 
eloquent writers, it is specially my province to endeavour to impress 
upon the reader the importance of endeavouring to form an estimate 
of the physical geography of the earth, during those remote periods 
when the Paleozoic deposits were accumulated, If very lofty 
mountains did not then exist, we have indeed, in this single pheno- 
menon, what may have been one of the chief causes of that equable 
and warm climate, so indispensably requisite to harmonize with the 
facts recorded in this volume. And if we add the inference adopted 
by many philosophers and geologists, that the earth, in cooling down 
from its original molten state, must, during long succeeding ages, 
have diminished in heat over its whole surface, we are enabled, by 
reference to physical changes alone, to satisfy ourselves that we 
have. in them the chief elements required to explain all climatal 
results. : 
“‘ From the effects produced upon my mind through the study of 
these imperishable records, I am, indeed, led to hope that my 
readers will adhere to the views which, in common with many con- 
temporaries, I entertain of the succession of life. For he who 
looks to a beginning, and traces thenceforward a rise in the scale of 
being, until that period is reached when Man appeared upon the 
earth, must acknowledge in such works repeated manifestations 
of design, and unanswerable proofs of the superintendence of a 
Creator.” 
NotTe.—We annex the following valuable table of the divisions of the older 
Rhenish rocks, as now understood by the geologists and paleontologists cited 
in the pages of Sir Roderick Murchison’s work, and whose discoveries, coupled 
with Sir Roderick’s recent observations, have led him to divide the Devonian 
rocks of the region into three parts. By having alongside of this table the gene- — 
ral succession of some rocks as classified by M. Dumont, the reader will at once 
see that although the mineral order, which that author indicates, is doubtless 
correct, no one of his three terrains is in un‘son with a classification based 
upon the distribution of organic remains, 
