THE STUDY OF CHEMICAL GEOLOGY. 
261 ' 
a steel anvil to the size of peas, then crushed in a diamond 
mortar, and afterwards pulverised in a wedgwood, or, preferably, 
in an agate mortar. 
In making chemical analyses of rocks, it should always be 
remembered that a few exact analyses are of far more value 
than a host of approximative ones, so that quality should never 
be sacrificed to quantity. 
All such rock examinations should include a careful descrip- 
tion of the mineral constituents of the rock itself, which, if fine- 
grained or compact, can only be effected by making a section 
and submitting it to the microscope. The physical properties, 
as specific gravity, &c., should also be noted, as well as, of course, 
the relations of the rock to the general geology of its district 
and the occurrence of any accessory minerals disseminated in it. 
It has been considered necessary to lay great stress upon all 
points connected with the selection and analysis of rocks, for, if 
these be not attended to, the labour bestowed upon them may 
be regarded as entirely thrown away. It cannot but be ad- 
mitted that the possession of a series of accurate and trust- 
worthy analyses of rocks is of almost vital importance to the 
advancement of chemical geology; and it is sincerely to be 
hoped that, considering the backward state of our knowledge of 
this subject in England, some efforts will be made to remedy 
this defect, and so provide correct data for advancing further 
research into this promising department of geology. 
In bringing forward this present short and necessarily ex- 
tremely imperfect attempt to introduce the subject of Chemical 
Greology to the notice and consideration of a wider public, it 
would be totally impossible, within the limits of the space at 
command, to treat, even superficially, of all the many important 
geological problems which require the aid of chemistry for their 
solution, such as, the distribution of the elements in the crust 
of the globe, the study of volcanic phenomena, the origin and 
nature of saliferous and mineral deposits, the metamorphism 
of rock masses, &c. The last of these subjects has ever been a 
stumbling-block to the field geologist, and has long proved to 
him a fertile field for speculation and discussion ; and even 
now, notwithstanding that so much has been written in its 
explanation, it remains, it must be confessed, nearly as obscure 
and intricate as ever. 
All manner of strange hypotheses to account for the meta- 
morphosis of rocks have, from time to time, been propounded, 
based upon the action of fire, water, electricity, magnetism, 
pressure, &c. ; in fact, upon everything conceivable, except upon 
a knowledge of the chemical composition of the rocks them- 
selves, in their altered and unaltered condition. 
In the remarks contained in the preceding pages, the main 
