Review of Phillips's Mineralogy. 43 
follows: em, cmrl, erm, crmle, crmleb, ermltzab, nreeq{mwlvab, 
tnezucrfmwvab. <A key to these letters is given in the earlier 
part of the work. Thus there are three modes of designating 
planes; one, by numbers, corresponding mainly in form, wit 
Weiss’s system, omitting the ratio sign, as 111, 012, 212, &e. ; 
another, the system of letters, just alluded to; and the third, the 
dots. . The first strikes us as the best, and, if slightly modified, 
as the only one required or needed, The others are perplexing 
to the student. 
‘The authors have added very much to our knowledge of 
the crystals of species by their measurements and calculations, 
and in this, the great merit and value of the work mainly 
consist. With each species, a large number of angles is men- 
tioned ; these angles are those between normals (perpendic- 
i to the faces, instead of those between the faces them- 
selves, 
_ The chapters on Refraction and Pleochroism are well drawn 
up, and the others on the Physical characters, though brief, are 
sufficient for the purposes of the Mineralogist. 
Under the head of Chemical Constitution, a classification of 
ne elements is given, in which, we judge, no attempt was 
made to present a view of the true chemical relations of the 
elements, 
_ Tu the chapter on Isomorphism, a 
as stated, ro Frankenheim’s “System der Krystalle,” presents 
alist of various isomorphous groups. This table might have 
been much extended by the results of later researches. For ex- 
have afforded additional facts bearing upon a branch of Iso- 
Morphism, not alluded to, : 
ee : 
* Vol, ix, 2nd Ser., p. 220. 
