734 
In connection with the subject of leucite rocks, Zirkel says : — 
“ More than twenty years ago, Alexander von Humboldt published his 
conclusion that leucite was a mineral only found in Europe ; and it is rather curious 
that this casual remark has not been disproved until very recently. This mineral, up 
to the year 1808, was only known as a constituent of several lavas of Italy, of the 
Laacher See, and of the Kaiserstuhl, in Baden. Since that year, it has been 
discovered to be a microscopical ingredient of many basalts of Saxony, Bohemia, the 
Thiiringer Wald, and the Ebon Mountains, occurring in unexpected frequency. But 
all these localities were European ; so the remark still held good ; and the other 
extra-European basic rocks, examined in largo quantity, were never found to contain 
leucite. 
“In 1874, Vogelsang discovered an Asiatic leucite. It occurred in a basaltic 
rock from the Gunung Bantal Soesoem, upon the small island of Bawean, north of 
Java. 
“ And now the microscopical study of the rocks of the Eortieth Parallel estab- 
lishes the existence in America of the most elassicl eucite rocks. Moreover, these 
rocks are richer in the mineral than any occurrence in the Old World, besides which 
their general composition is very peculiar. Leucite was always considered, as is well 
known, one of the most perfect members of the regular system, until, in 1872, G. vom 
Hath staled that it belonged to the tetragonal or quadratic system, the apparent 
icositetrahedron being a combination of The colourles.s crystals, which 
generally show in the section a more or less regular or rounded octagon, have the 
peculiarity of containing a great quantity of strange little, crystals and grains grouped 
into a small central heap or (which is more often the ease) concentric zones, of which 
the sections are also octagonal or roundish. These corpuscula, which are supposed to be 
intruded into the leucite, are, instead, situated on the surface of the leucite forms or 
globular figures.”* 
Teall states that leucite has not yet been found in Britain.f 
The “Mitre Hock ” sample from New Guinea is to be noted on account of the 
abnormally large size of the augites, many sections of which happen to be cut parallel 
to the plane of symmetry (010) or »?». The other Queensland basalts of this 
collection call for no special remark, although some, like the Herberton basalts, are 
highly typical rocks. But the three samples from New South Wales (two from 
Bathurst, and the other from Mount Sassafrass) are, -par excellence, the basalts of the 
whole collection. Some of ZirkeTs excellent drawings in “ Microscopical Petrography,” 
quoted above, might almost be used to illustrate theit textures. 
The dolerites of the Sellheim Eiver are so rich in apatite that one cannot fail to 
be struck with the sections, with their brilliant little water-clear hexagons appearing as 
black as ink, of course between crossed nicols. 
Lastly, the Mount Kinchant (Mackay) sample is of interest, as it is pretty fresh, 
and its felspars very much banded and pellucid. 
DIORITES AND PORPHYRITES. 
Diorite proper is a crystalline-granular mixture of plagioclase felspars and 
horneblende, while porphyrite is characterised by a granular base of plagioclase felspars, 
and either hornblende or augite, in which base are developed larger crystals of the same 
minerals. There is, therefore, a inineralogical connection between the two groups, 
though structurally they are different. Professor Hutton uses the word “ porphyritic” tor 
* “ Microscopical Petrography,” p. 259. 
t “ British Petrography.” Note on Fig. 2, Plate xli. 
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