190 
ME. X. STOEY-MASKELYXE OX THE 
are the ingredients of the stone. From the former class, we learn that a meteorite has 
had a history that it has undergone change subsequently to its first consolidation in its 
present form. The crystalline character of all the constituent minerals ; the fissures at 
one time formed, then filled and then, in many cases, broken across and ‘ heaved ’ and 
filled again, like some mineral lode ; the £ chondritic ’ structure that G. Rose has illus- 
trated*; the fracture, in at least one meteorite, of the spherular ‘ chondra,’ which have 
been split and severed and recemented into a compact mass, — these are among the 
many facts imprinted on a meteorite which are so many records belonging to its history, 
and which by the aid of the microscope we may read and interpret. But to found a 
classification on the structural characters of meteorites is not the same thing as to arrange 
them according to their mineralogical composition. The two must be combined for a 
philosophical arrangement. 
I propose dealing with the mineralogical side of the problem in the present memoir, 
and to recur hereafter to the structural composition of meteorites, when the nature ot 
their ingredient minerals shall have been rendered clear. 
The general features of the microscopic sections of certain meteorites were described 
by me in the years 1863-64 ; and the examination in this way has been extended to 
above 140 distinct aerolites. The crystallography, however, of the numerous crystals 
seen in such a microscopic section is almost hopelessly difficult. In cases where crystal- 
lographic directions are indicated by cleavage-planes or by the ‘ traces ’ on the section 
of determinable crystal faces, some conclusion as to the symmetry and system of the 
crystal can be drawn from the directions of its optical principal sections as indicated by 
light polarised in a known plane. And occasionally a section is met with so nearly 
parallel to one of the important faces of the crystal as to allow some reliance to be placed 
on the angles of its bounding planes as measured by a delicate eyepiece goniometer. A 
long series of measurements and determinations of the directions parallel to the principal 
sections in the crystals met with in these microscopic slides has convinced me that, how- 
ever useful the microscope may be in revealing the structure of a meteorite and helping 
to determine its place in a collection of such bodies classified according to their physical 
constitution, it is only partially of use in determining the mineralogical character of the 
constituents. But if the applications of polarised light and the eyepiece goniometer are 
thus limited, the microscope has another function to perform in such an investigation; 
for, from the carefully bruised debris of particular meteorites selected for the frequent 
recurrence in them of recognisable minerals, and for the magnitude of the grains of these, 
one is able to pick out under the microscope the distinct particles of each such mineral. 
Such particles occasionally offer cleavage-planes, or even a crystal face or two, to the 
goniometer. In a very few cases crystals have been found sufficiently complete to lead 
to a reliable crystallographic result f. The chief advantage of this method is, however, 
* Abliandl. der Konigl. Akademie der Wissensch. Berlin, 1864, p. 84. 
f The crystals of Anorthite in the Juvinas Meteorite were thus measured in the British Museum by my late 
colleague, Professor Y. von Lang, Sitzuugsber. Akad. der Wissensch. Wien, 1867. 
