Se Nigh es of Rocks and Minerals. 105 
A microscopical examination of thin sections shows that all these 
rocks belong to the same type; they do not in fact differ more from 
each other than do different specimens of any one of them. ‘The 
Toadstone of Derbyshire is merely an amygdaloidal variety. 
The rocks of the Warwickshire coal-field differ considerably 
from the foregoing ; they contain hornblende instead of augite, and 
are therefore true greenstones or diorites; they may be readily 
examined in the railway cutting near Nuneaton, and also a little 
to the west of Atherstone. All the rocks just enumerated are 
clearly older than the surrounding Permians, which are never pene- 
trated by them. 
Having now made upwards of four hundred sections of rocks 
and minerals, I am inclined to believe that the following results of 
microscopical examination will stand the test of further study. 
1. The mineral constituents of the melaphyres and other fine- 
grained igneous rocks may be determined with certainty—a result 
which has not been attained by any other method of examination. 
2. The mineral constituents of the true volcanic rocks, and those 
of the old melaphyres, are generally the same. 
3. The old rocks have almost invariably undergone a consider- 
able amount of alteration, and this change alone constitutes the 
difference now existing between them and the more recent volcanic 
basalts. 
The basaltic lavas of the Rhine and Central France are com- 
posed of a triclinic felspar, augite, magnetite, olivine, and frequently 
apatite, the same minerals as those constituting the old rocks above 
described. I have fine-grained specimens of the latter hardly dis- 
tinguishable from recent basalts ; and a section of Dolerite from the 
Puy de Barnére, in Auvergne, does not differ in any important 
particular from coarse-grained specimens from Rowley. 
It would be easy to extend the parallelism to other classes of 
rocks, but I will now only observe that we have here another proof 
of the doctrine long taught by Lyell—the uniformity and continuity 
of the Laws of Nature. 
|The foregoing important contribution is taken from the ‘ Pro- 
ceedings of the Birmingham Natural History and Microscopical 
Society, a most interesting volume, just published.—Ep. M. M. J.| 
