On the Minerals of Trap and the allied Rocks. 59 
It has been altogether too common among geologists to treat min- 
eral information with a degree of neglect almost amounting to 
contempt, although, as facts will probably hereafter show, they 
lie at the basis of an important branch of geological science. 
But to proceed with the subject before us. We find that 
Quartz or chalcedony, and datholite, very seldom overlie other 
mineral species in geodes or amygdaloidal cavities, while the lat- 
ter often overlie them.* 
Prehnite is usually lowermost with reference to all the species 
except the two just mentioned. Occasionally it is found upon 
analcime, as at the Kilpatrick hills. 
Analcime is commonly situated below all, except quartz, datho- 
lite and Prehnite. 
Of the remaining species, chabazite, stilbite, harmotome, Heu- 
landite, scolecite, mesole, Laumonite and apophyllite, it is more 
difficult to distinguish an order of arrangement. My investiga- 
tions only enable me to state that chabazite is usually covered by 
the rest, (when associated with them, ) yet it is sometimes super- 
imposed on stilbite; and apophyllite is almost uniformly above all 
with which it may be associated ; cale spar is at different times 
above and below. We thus arrive at the following as the usual 
order of superposition. 
1. Quartz. 
2. Datholite. 
3. Prehnite. 
A, Analcime. 
5. Chabazite, harmotome. 
6. Stilbite, Heulandite, scolecite, natrolite, mesole, Laumo- 
nite, apophyllite. 
It is a reasonable inference that the species which covers the 
bottom of a cavity was first deposited, and, as a general rule, that 
the others above were formed, either simultaneously, or in succes- 
sion upon the lowermost, as their order,may indicate. Each is 
usually perfect in its most delicate crystallizations, so that we can 
not suppose that the miuerals first deposited often underwent 
change after their deposition, though instances of this may no 
doubt be detected. 
It is also evident that if there were any species formed previous 
to the complete cooling of the rock, or if any require for their for- 
* The writer has observed stilbite, apophyllite, cale spar and Prehnite overlying 
datholite, and various species over Prehniie. 
