Mineralogy, Geology, &c. 45 
stone ; these cavities are often brilliantly studded with them, 
and doubtless it arose from their falling out by the disinte- 
gration of the rock that the crystals were formerly found, on 
the shores of the island and in the water. At present they 
are scarcely obtained at all except by breaking the rocks. 
The immediate matrix of the crystals seems to be a mixture 
of fine granular quartz with the limestone ; it is impressible 
by steel, but sometimes does not effervesce with acids.* The 
erystals of this locality are of the common form, very lim- 
pid, and often contain a dark coloured foreign substance im- 
bedded in them. 
Crystals of calcareous spar, well defined and of considera- 
ble size occur in the same rocks, sometimes with the quartz 
crystals, and sometimes “by themselves; they appear to be 
modifications of the rhomboidai varieties. 
Very brilliant rhombic masses of calcareous spar also pre- 
sent themselves in these rocks; these masses are not-crys- 
tals, but have the crystaline structure, giving perfectly rhom- 
boidal fragments with a high pearly lustre; they are very 
white and appear exactly like the Iceland crystals, only 
they are not transparent. ‘They seem to be the bitterspath. 
The poor people on the island had no idea that the calcare- 
ous crystals were of any value, and had been in the habit of 
throwing them away; we took care to give them a different 
impression, and trust it may be useful to future visitors. 
Crystals of Diamond Point. We passed down the whole 
length of the lake, (thirty-six miles,) in a very small open 
boat—a fisherman’s skiff, rowed by two men. We stopped 
at a place on the north shore of the lake, called Diamond 
Point, from the fact that crystals are found also at this place. 
It has been recently opened by the man who lives on the 
island, and who was our guide on the present occasion. 
The rock and its associated minerals are the same as on the 
island, only we observed a greater variety of siliceous mine- 
rals ;—portions of calcedony and hornstone and agate—ele- 
gant cavities occupied by quartz crystals, and some singular 
banded portions, concentric and curved like agate, but 
* It commonly effervesces, and feebly scratches glass. 
