ee er NEN fee ae Se ee a Pe mma ae e e  s Se RN Set Pe ee ee eg ee EN Spee Kw Se Poe fe 
E. &. Dana on the Datolite from Bergen Hill, N. J. 17 
which serves to distinguish them at a glance from all other 
forms. It is always els: no further modifications than those 
fgared having been observ 
Another and more snteretinig type is shown in figure 2. 
Tho crystals here are approximately equal in the three dimen- 
sions. The figure shows this form in its simplest condition. 
Other planes occur, viz: —2-7; also (as in fig. 3, which is a por- 
tion of a crystal with this habit) 2-1, 4-2, 4, 4, 3, 44, -8-2 ; these 
the crystals. 
c. Higure 14 represents a rare and quite unique form. The 
planes —2-2 and 2 are here most prominent, and when the J be- 
comes merely a line and 7-2 a minute triangle, as is sometimes 
the case, it has the aspect of a rhombohedron. The planes 2-2 
and 2-9 are noticeable features of the figure, and are spoken of 
more particularly in another place. In addition to the planes 
figured, there occur on crystals of the same specimen, 1 very 
small, and 7-2, 7-2, 2-2 as mere lines. 
d. Another type of form, though not so distinct, is exhibited 
in figure 13. Under this type we seldom find the crystals of 
two specimens exactly similar, there being a great variation in 
the relative sizes and in the number of the P dene A very 
complex form of this type is bY. ager in fig. 8. € spec- 
ial points to be noted in crysta this habit are: the plane 
-2-4, which is often very large and almost invariably etched 
and therefore without pote and also the presence of the series 
—4-2, —4-4, —4-7 and —6-3, ~6-8, - 6-7 (fig. 4). The planes of the 
series last rietioad are very common, the two series frequently 
occurring together; and one of them at least is almost always 
present with the —2-. This peculiar range of planes above 77 
oe not appear to have been met with on crystals from foreign 
ocalities. 
Under these four distinct types and their modifications, all 
the crystals of Bergen Hill datolite observed by the writer (on 
over two hundred specimens) can be includ 
e following is a list of all the planes obseryed ; in it, those 
marked with an asterisk (*) have not "been observed before: 
O (top) vertical prisms, q-t, 0-4,* 7-2,* Z + 1-2, ne * 44> or 
thodomes, —1-i, —4-2, —2-i, —4-4 8-1; 24; clino- 
domes, 4-4," 1-4, 4, *92 i, 4-2; ” hemi- at —4; ay dy 
i, $5" —42, 44 6-3," —6-3; 4-2;* _ 6-3 (?), 12-3; 
— $3, —8-2, 39 9-2: —4.3,* 33* 23: -& 219.* 3.5,* 9.4% (?), 
s* @).+ 
BA The plane 6-7, found by Hessenberg (Min. Not., rv, where it is designated 
#P «) on — from Bergen Hill, I have not observed except on crystals from 
Am, Jour. Sou —Tarxp Srrtss, Vou. IV, No. 1.—Juty, 1872. 
