34 Dr. Mac Culloch on 



at St. Jago or at Brava, which is contiguous to Fogo, and 

 frequented for its wines — the same I presume as are called 

 Cape wines, although said to come from the Cape of Good 

 Hope. 



John Hancock. 



On Classifications of Rocks. — By J. Mac Culloch, M.D., 

 F.R.S., &c. 



In every branch of natural history it has been a principal 

 object to adopt such arrangements of the bodies of which it 

 treats, as should facilitate their study. The most purely arti- 

 ficial classification may thus be useful ; but the naturalist of 

 higher views attempts to discover the order which Nature her- 

 self has instituted^ and thus, if possible, to combine, with 

 utility, the history of those analogies which form the basis of 

 all science. 



Such is the wide and various range of geology, and so im- 

 portant are the great relations and analogies which it involves, 

 compared to those which regard only its minuter details, that 

 it has been the object of almost all the cultivators of this 

 science to found, at least, the chief features of its classification 

 on certain leading relations. As the essential circumstances 

 involved in this question do not admit of being examined in 

 this paper, the reader must be supposed to understand the 

 following statements, without entering into much minuteness 

 of detail. 



Though presenting to the eye infinite varieties of aspect, 

 the real and definable differences of rocks are very limited. 

 Hence, no great number of names has been required for dis- 

 tinguishing them. It is also found, that in a single mass or 

 stratum of one rock, bearing one fixed and steady relation to 

 its associates in nature, the aspect, the proportions, the mode 

 of mixture, and the nature of the ingredients, are subject to 

 variations ; and hence a still narrower limitation of the num- 

 ber of names, which a superficial consideration might have 

 been inclined to apply to them, has been found necessary. 



