226 Messrs. Jackson and Alger on the 
three eighths of an inch in diameter.. But usually the crystals are 
modified by the absence’of solid angles and replacement jof 
single planes, which, by their extension, tend to produce common 
six-sided pyramids. The amygdaloid is traversed by narrow and 
indistinct veins of specular iron ore, sometimes hollow, and en- 
closing white transparent chabasie. Not unfrequently, insulated 
crystals of the specular ore are imbedded in limpid chalcedony, 
thus forming a singular variety of agate. 
But a substance more likely to interest the mineralogist at 
this place, is laumonite. This curious mineral presents itself, trav- 
ersing the amygdaloid in veins sometimes a foot wide, running in 
vertical, inclined, and zigzag directions. The substances of these 
veins, especially the crystals, are more or less decayed, in situa- 
tions most excluded from moisture ; and the best specimens were 
found only in those places which were regularly covered by the 
tide. Into the cavities of these veins, the laumonite projects in 
beautiful groups of crystals, which exhibit the form of the prima- 
ry oblique rhombic prism, firmly implanted at one extremity, and 
at the other terminated by a single rhombic plane, inclining from 
one acute angle to the other. The crystals are colorless and 
transparent, and frequently an inch in length. The calcareous 
spar which forms the walls of the veins, is often scattered over 
these groups in insulated rhomboids, considerably more obtuse 
than the primary crystals, and exhibits examples of hemitropic 
combination. Interspersed also with these, are brilliant span- 
gles of specular iron ore, which give much additional beauty to 
the specimens, and serve at the same time to support the crystals 
of this fragile mineral. It is not a little singular that we have been 
unable to discover, in the form of the crystals of laumonite, the least 
modification by the absence of either edges or solid angles; while in 
