Mr Brooke on Comptonite^ Brewsterite^ and Heiilandite. 113 
class of primary forms, in the facility with which it cleaves pa- 
rallel to the terminal plane, and in the constant brilliancy of the 
planes developed by this cleavage. Fig. 3. contains all the mo- 
difications I have observed on the crystals I have examined, the 
angles at which some of the planes incline to each other mea- 
suring nearly as follows : 
P on a^ 
93° m 
h 
119 30 
c. 
114 30 
^d, 
112 
e. 
92 
a — a', 
172 
a — c. 
\ 95 
a! — c , 
j 
Finding on several crystals the planes c, c', larger than any of 
the others, and on one crystal finding those planes alone, I have 
taken them to fix the ratios of two of the edges of the prism. 
Supposing them to result from a decrement by one row on the 
edge n o, the edges np to nm would be as 35 to 16. And if the 
planes a, a' be supposed to result from a decrement by four rows 
in height on the edge nm the terminal plane, the ratio of 
np to no would be as 35 to 10. 
On examining the Abbe Haiiy’s varieties of Stilhitey I have 
found, that those which Werner distinguished by the names of 
Radiated and Foliated Zeolite, are two distinct species ; and I 
am happy in the opportunity which this discovery has afforded 
me, of associating the name of Mr Heuland more intimately 
with mineralogy, by calling one of the substances Heulandite^ 
and of thus recording the readiness with which Mr Heuland 
has on all occasions opened his cabinets to the researches of 
science, and his very liberal cqntributions of specimens, w hen- 
ever they have been required, for the purposes of either chemical 
or crystallographicaj examination IJhe first of the two species 
of the Abhe Hauy’s Stilhite^ from which he appears to have de- 
* We cannot omit the present opportunity of adding our testimony to the libe- 
rality of Mr Heuland, and to his unceasing zeal for the progress of his favourite 
science. It is fortunate for mineralogy, that the possessor of one of the finest col- 
lections in Europe, should be a most generous dispenser of its benefits for the puiv 
poses of scientific research. — D. B. 
VOL. VI. NO, 11. JANUARY 182^, H 
