332 



THE GEOLOGIST. 



ing 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.GkS* 



The rocks composing the earth's crust contain a history and re- 

 present time — a history of changes 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 Paleozoic 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 



* Being tlie substance of six lectures delivered at the Royal Institution from 

 May to June, 1861. 



