1823.] Geological Transactions of Cornwall, Vol. II. 295 



poses, but as tending to elucidate some of those more difficult 

 and interesting subjects of geological research, respecting the 

 true nature of which there is such a diversity of opinion. A 

 considerable portion of the volume is occupied by four papers 

 on the temperature of mines, the contents of which we shall not 

 advert to in the present article, as a memoir on the subject will 

 shortly appear in the Annals, containing a full account of the 

 facts which are detailed in them. Before we proceed to a brief 

 analysis of the other papers, it may be well to state, from the 

 preface, that the construction of a geological map of Cornwall, 

 intended, according to the wishes of the Society, " to show not 

 only the varieties of rocks, but also the locality and position of 

 the principal metalliferous veins, and the cross-courses which 

 intersect them, has already occupied much of the time and 

 attention of some members ; " but this, it is observed, " is an 

 undertaking of immense extent and labour ; and the map of the 

 lodes in one parish (St. Just) given in the present volume, will 

 at once show the nature and importance of the plan, as well as 

 the time requisite for the completion of such an undertaking." 



I. On some Advantages which Cornwall possesses for the Study 

 of Geology, and on the Use which may be made of them. By John 

 Hawkins", Esq. FRS. &c. Hon. Mem. GSC. 



The advantages of Cornwall for the study of geology, are 

 stated in this short paper to arise from its being a primitive 

 country, having greater facilities for observation than any inland 

 country can possess ; and from the immense extent and import- 

 ance of its mining concerns. In illustration of some remarks on 

 the vague use of language in this science, the following state- 

 ment is given. 



" It is long since the attention of geologists has been drawn 

 to the disposition observable in every distinct rock mass, to 

 separate in a form which is in some measure characteristic of its 

 composition ; although to this day, as far as I know, no general 

 name has been given to this phenomenon. By some who have 

 noticed a degree of uniformity in the angles resulting from the 

 inclination of so many plane surfaces, it has been confounded 

 with crystallization, and by others, on rather better grounds of 

 reasoning, with stratification ; although from the first it differs 

 in the very material point of the structure of its mass, which is 

 not one crystal, but an aggregation of crystals ; and from the 

 other, in that of continuity. It seems to be the effect of the 

 contraction of matter at the period of its consolidation, and is 

 common both to the volcanic and the Neptunian formations ; 

 and this theory derives a further confirmation from the influence 

 which the size and form of the aggregated parts of the mass 

 have in the mode of its division. 



" I know of no better generic name for this distinctive cha- 

 racter, than that of articulation, while most of its specific forms 

 might be expressed by the terms prismatic, cuneiform, rhom- 



