Siluria—Present State of Geology. 313 
Stluria—Present State of Geology. 
The geologist is now in possession of a vast amount of 
- facts bearing on the history of the earth’s structure, and the 
different epochs that extinct organic beings appear to have 
passed through ; and the most important of these facts have 
been studied with a strict philosophic spirit, and sound prac- 
tical results have been drawn from them, and are now of 
the utmost advantage for the progress of both science and art. 
No man of science deserves a deeper debt of gratitude 
from his country for the services he has rendered to it 
than Sir Roderick Murchison. Sir Roderick did not only 
lay down his military profession, but sacrificed a large por- 
tion of his great fortune, and the best part of his valuable 
life, in exploring the structure of what all must admit to 
be the most difficult part of the earth’s crust, viz., the pro- 
tozoic, or the first epoch of organic existence. On this 
epoch, Sir Roderick has thrown more light than any man, 
either dead or alive. After long, unwearied labour, and 
with a fixed determination, he has arrived at the same 
result as to the protozoic epoch as the immortal Cuvier had 
done before him with the tertiary epoch. 
To be the discoverer and the historian of a period of the 
world’s history when the first organic beings were called into 
__ existence on our habitable globe, is surely what any man 
___would be proud of. But our intellectual and noble veteran 
has still a good deal to do before he completes his picture of 
the Ancient Siluria. He has to give us a better notion of 
the ancient Silurian meteorology and climate—of the pro- 
bable amount of solar heat required at that time for the de- 
velopment and growth of the vegetable and animal organic 
beings—and laws of geographical distribution. Such kind 
of knowledge is necessary to enable us to arrive at correct 
conclusions. We have, during the present period, many 
changes taking place, the conclusions in regard to which 
would certainly be incorrect if we were guided simply by 
the law of deposition. For example, we find, on a tropical 
‘coast, strata deposited daily from one of the great rivers; 
