2 Proceedings of the Royal Physical Society. 
various minerals wliicli compose entirely or are products of 
the rocks ; palaeontology, on the other hand, has only to do 
with the organisms so profusely found in the strata from the 
Azoic, through the whole range of the Palseozoic series. 
Petralogy, which mainly studies the superposition and 
ages of rocks, has, since the days of Dr William Smith, re- 
ceived its principal facts from the labours of the palaeonto- 
logist. 
The balance of the mineralogist and his goniometer have, 
during those last fifty years, been sadly ignored and over- 
looked by the geologist, who is ever and anon boasting that 
he studies in the field, and has no faith in the teachings of 
mere hand specimens in the closet. That this is true, I 
quote from the first line of the first chapter of the last, and 
certainly the best book lately published on the subject, 
namely, " Jukes' Manual of Geology," where he states, — 
" Lithology, or the study of the mineral structure of rocks, 
is based on mineralogy. ... In order to understand litho- 
logy, however, an acquaintance with mineralogy in general, 
though always useful, is by no means necessary, since the 
minerals which enter into the composition of rocks are very 
few compared with the whole number of minerals. But as 
regards these few minerals, it is their chemical compo- 
sition, still more than their physical characters, which we 
have to regard in their lithological relations. It is there- 
fore absolutely necessary to understand so much of che- 
mical nomenclature and chemical laws, as shall enable us 
clearly to comprehend the precise meaning of this chemical 
composition. 
"As, however, geologists, from the very nature of their 
pursuits, are unable to devote much of their time to closet 
study or laboratory work, unless at the expense of their own 
more proper field of investigation, I will here endeavour to 
assist the student by giving him a condensed abstract of so 
much of the elements of chemical mineralogy, as may 
enable him to understand rightly the lithological descrip- 
tions which follow." The reader of this most admirable 
work will find this sentence, which I now quote as germane 
to our subject, in page 8 of the introduction, and which, 
