viii 



INTRODUCTION. 



Structures. This, the most important part of the arrangement, being 

 thus borrowed from chemistry, which like a guardian angel 

 should always hover round and direct the labours of mine- 

 ralogy ; the other subdivisions only require a characteristic 

 clearness to assist the memory (the chief object in any system 

 of natural history), and an appropriation to the subject, so 

 as to satisfy the judgement and imagination. From the 

 earliest productions of Linnaeus to the present time, the 

 word STRUCTURE has been applied, with classical propriety, 

 to denote a most striking and characteristic distinction be- 

 tween mineral substances, whether on a great or on a small 

 scale. Linnaeus has observed that there are only three great 

 roads which can conduct the curious traveller through the 

 mineral kingdom ; that of Physics, or Natural Philosophy, 

 which treats of the obscure generation of stones ; that of 

 Natural History, which examines their evident structures ; 

 and that of Chemistry, which considers their analyses *. A 

 term thus strictly appropriated, and, as it were, consecrated 

 to the science, has therefore been selected for the next char 

 racteristic subdivision. 



But as Werner and his disciples not only admit the various 

 earths, as so many Genera ; and their Modes, or the modifi- 

 cations of the mixtures, and even colours, as so many Spe- 

 cies , but also what are, with great penury and uncputhness 



Aspects. 





* <{ Via triplex tantum per Regnum Lapideum curiosos ducit : Physica qua 

 descendit per Lapidum obscuras Geneses. Naturalis quae excurrit per Lapidum 

 apricas Structures. Chemica quae adscendit per Lapidum destructivas Analyses ." 

 Linn. Min. aGmelin, p. 14. 



In the* edition of his System, Holmise 1768, Linnaeus has the following 

 among the external characters : " The Structure, foliated, fissile, convergent, 

 in fragments." Werner says limestone is of a simple structure. Dr. Thomson, 

 in his valuable Chemistry, says that gneiss differs in its structure from granite ; 

 and that the structure of mica slate is thinly schistose. It is chiefly judged by 

 the fraeture; and is as applicable to small specimens, if well chosen, as to the 

 rocks themselves : it may be earthy, compact, columnar, large-grained, &c. &c. 

 In .classical Latin structura is not only applied to the largest edifices, but in very 

 minute senes ; as structura versuum, structura yerlorum. 



