332 
THE GEOLOGIST. 
ino- was devoted to the consideration of the best kinds of hammers, 
let the next produce some scheme for using them to some purpose. 
We wish the Society well, and it is therefore in true friendship we 
urge it to assume the proper dignity of labour for which it is so 
admirably suited. 
ON THE DEVONIAN AGE OF THE WORLD. 
By W. Pengellt, F.G.S.* 
The rocks composing the earth's crust contain a history and re- 
present time — a history of charges numerous, varied, and important : 
changes in the distribution of land and water ; in the thermal 
conditions of the world ; and in the character of the organic tribes 
which have successively peopled it. The time required for these 
mutations must have been vast beyond human comprehension, 
requiring, for its expression, units of a higher order than years or 
centuries. In the existing state of our knowledge it is impossible to 
convert geological into astronomical time : it is at present, and 
perhaps always will be, beyond our power to determine how many 
rotations on its axis, or how many revolutions round the sun the 
earth made between any two recognised and well-marked events in 
its geological history. Nevertheless it is possible, and eminently 
convenient, to break up geological time into great periods : it must 
not be supposed, however, that such periods are necessarily equal in 
chronological, organic, or lithological value ; or separated from one 
another by broadly marked lines of demarcation ; or that either their 
commencements or terminations in different and widely separated 
districts were strictly synchronous. 
One of the terms in the chronological series of the geologist 
is known as the Devonian, that which preceeded it the Silurian, and 
the succeeding one the Carboniferous period ; and these, with some 
others of less importance, belong to the Palaeozoic or ancient-life 
epoch, or group of periods. The Devonian is, therefore, a chapter — 
it may be called the middle chapter — in the ' first volume of the 
organic history of the earth. It is this chapter, containing the 
history of the " Devonian Age ot the World," which is to furnish 
material for this article. 
The period takes its name from the fact that it represents the era 
* Beiag the substance of six lectures delivered at the Eoyal Institution from 
May to June, 1861. 
