2 Proceedings of the Royal Physical Society. 



various minerals which 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 Palaeozoic 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, 



