358 Mr. Playfair’s Account of a 
case that determined us to take one stone and reject another, 
could only be perceived by an observer on the spot, whose 
eye was accustomed to judge of the varieties, the plenty or 
the rarity of the minerals that passed in review before him, 
by indications which it is impossible to describe in words. We 
are here therefore with reluctance compelled to request from 
the reader more credit than we are able to prove to him that 
we deserve. We know that in doing; this we are craving: an 
indulgence which no wise and candid observer ever wished to 
possess ; we sincerely regret that the nature of the subject 
forces us to make this demand, and that the part of our work 
which it was most difficult to perform to our own satisfaction, 
is quite incapable of being explained to the satisfaction of 
others. 
Catalogue of Specimens from Schehallien. 
The rocks of the mountain may be divided, as already re- 
marked, into three classes ; granular quartz ; mica, and horn- 
blend slate ; granular limestone. The specific gravities were 
ascertained by the late Dr. Kennedy, and it is therefore un- 
necessary to add that their accuracy may be perfectly relied 
on. The pieces weighed were between 1000 and 4000 grains: 
most commonly between 2000 and 3000. Different pieces of 
the same specimen were often examined. The water used 
was distilled, and always of a temperature between 60 and 61 
degrees. 
Quartz. 
1. Gray sandstone containing mica in thin layers. Specific 
gravity = 2.6435. 
2. White quartz, very pure. Fracture vitreous. Occurs in 
