128 Scientific Intelligence. 
ordinary galena might have an octahedral as well as cubic cleavage, — 
that the first might be so marked by the great facility of the last, as 
the cube angles. id not succeed in taining this cleavage with 4 
chisel and hammer, for when I struck in the direction of the octahedral 
plane, I immediately knocked off a number of small cu u 
crushing in a steel mortar small cubic masses of the mineral, I could pick 
out among the fragments occasionally one with octahedral planes like 
the two I enclose. As tl atter stands now, it would appear that 
hedral is ga easier. The oc ciel cleavage is therefore nothing ab- 
normal, b rely an eal development of a constant condition. It 
will not, therdite I think, be necessary to resort to any pseudomorphism 
to explain this peculiarity, which entirely disappears in this new view of 
e case. May not the cause of this unusual facility of the octahedral 
cleavage in this new variety be simply the pressure to which the vein has 
been subjected? My experiments with the crushing mortar look - 
Sates prone” > Sativew:. a subsequent letter, dated April 11, i362, 
Prof. Cocke gives at results “of his experiments with a hydraulic press. 
The galena from ie when crushed in a steel mortar with this 
was found to give numerous examples of octahedral cleavage eng while 
that from Freiberg gave very few, so “that it was necessary to hunt for 
some time to find one.” Some specimens also gave indications of what 
appeared to be a dodecahedral cleavage. 
Although Prof. Cooke’s results apparently indicate shh galena has an 
octahedral as well as a cubic cleav vage, still the reas of the es 
per tego to the octahedral ~ should be thus produced. We 
t that of hi i 
varieties. Haidin f has observed that the pre fluor from Ae 
metric species may also show this double and triple cleavage, but we are 
not aware that ay ag pe ~ been weal where the cleavag® 
the Lebanon 
jae translation of the Treatise on Mineralogy by F. Mohs, vol. ii, p- 69, 
Edinburgh, 1825. 
