318 On the Emery of Commerce. 



glacier mud, of streaked pebbles, of arctic shells, and of 

 raised beaches covered with existing shells. 



If this attempt at explanation does not ensure the convic- 

 tion of the reader, I trust that he will at all events concede 

 that I have been very moderate in the use of hypothesis. I 

 have compared Scotland to a country of an analogous eleva- 

 tion, where the ancient extension of glaciers is completely 

 realised ; I have based my explanation upon the striated 

 rocks, the boulder clays, and the striated pebbles — upon the 

 observation of existing glaciers ; I have demonstrated the sub- 

 sidence during the glacier epoch, by the arctic shells, and the 

 emersion after the termination of the cold epoch, by the raised 

 beaches covered with modern shells. If, then, I have deceived 

 myself, I need fear only as it regards my deductions, for the 

 observed facts which I have invoked have been very often 

 verified by competent observers. 



On the Emery of Commerce, 



The emery of conimerce, properly speaking, is not a simple 

 mineral, but a compound of granular corundum and oxide of 

 iron, in which the former usually predominates. The oxide 

 of iron present is under the form of magnetic oxide, more 

 or less mixed with iron glance ; sometimes it is titaniferous. 

 The aspect of the substance differs considerably according 

 to the locality. 



The emery of Saxony is of a bluish grey colour, and is in- 

 termixed with talc and steatite. 



The Naxos emery is of a bluish grey, with a mottled surface, 

 with small points of a micaceous mineral disseminated. 



The Gumuch-dagh emery is commonly of a fine grain, and 

 dark blue, bordering on black, not unlike certain varieties of 

 magnetic iron ores. With this variety we frequently find 

 pieces of corundum of some size. The interior of the mass 

 is tolerably free from the micaceous specks found in that of 

 Naxos. 



The Kulah emery is usually coarse-grained, and much 

 darker than that of Gumuch-dagh, its external surface re- 

 sembling sometimes that of chromate of iron. 



