14 Account of the Kaatskill Mountams. 
more stratified. In these rocks several feet below the sur- 
face, are many cavities partially filled with a black mud. In 
this mud, large quantities of these crystals are found, varying 
‘m size froma pipe stem, to several inches in diameter. 
‘These crystals are commonly imperfect, presenting a sur- 
face with several sides polished. ‘They usually have cavi- 
ties in them, partially filled with mud, probably owing to 
the particles when ina state of solution, not being near 
enough to attract each other. Several crystals containing 
water ina fluid state, have been found in this hill. This 
water appears in a cavity in the crystal, which is filled with 
this fluid and air. I have one found here, in which, by 
changing its position, the air will rise in the tube, causing 
the water to descend. In number IV. of the “ American 
Journal of Science” is a description of a crystal of this kind, 
found in this hill. Professor Dewey who describes it, sup- 
poses the liquid to be naptha, from the fact that the “ fluid 
did not freeze.” I have seen several crystals from this hill 
of this kind, and as far as I could form an opinion from the 
appearance of the fluid as seen through this transparent me- 
dium, I have supposed it to be water. As these crystals lie 
in a black mud several feet below the surface, it would seem 
improbable that Naptha should have been found mingled 
with it, particularly as the rocks around it bear a strong re- 
semblance to argillaceous slate. ‘This oil is rarely if ever 
found pure, and when pure is usually associated with Car- 
bonate of Lime. A specimen of this kind- belonging to a 
friend of mine, when exposed to an atmosphere 6° or 8° below 
zero of Fahrenheit, congealed. As the water filled most of 
the cavity, it expanded during congelation, so as to burst 
the crystal, and the liquid which had every appearance of 
water evaporated. ‘The fate of the crystal was not known 
until some time after the evaporation of this fluid. ‘The 
large crystals are seldom transparent, owing to the mud and 
riffs beneath the surface. ‘Those of a small size are gene- 
rally transparent and perfect. ‘The common form is a six- 
sided Prism, terminated at each end, by a six sided pyra- 
mid. ‘These crystals are frequently irised, presenting all 
the colours of the Iris, owing to the fissures under the sur- 
face. Ihave seen-several specimens of Twin crystals that 
were found in this hill, united to each other at one of their 
edges. 
