f 152 ) 
A leucite basalt, rich in magnesium, is the type from Bongsberg near 
Pelm in the Eifel (YI), which contains much olivine whereas the 
forming of biotite shows a certain relation to that of the olivine 
crystals, for the former are only found deposited round the latter; 
the complete freshness of both minerals makes an alteration of one 
into the other improbable; a simultaneous origin is indicated. 
On comparison with the “Minette of Highwood type” or “mica 
basalt” of the Highwood Mountains (II) we see that here the proportion 
of alkalies to silica by an equal content of Al a O t would have been 
in itself more favourable for the formation of leucite, whereas this 
mineral only occurs in a subordinate proportion in the matrix on the 
side of alkali felspar. This minette contains but little, olivine and also 
has augite among its phenocrysts. The biotite occurs as well in the 
matrix as also as phenocrysts, and in the latter case the slightly 
pleochroitic pale yellowish brown crystals are surrounded by a dark 
border of much stronger pleochroism, corresponding with that of the 
biotite of the matrix. In this case also there are therefore two distinct 
periods of mica formation, the first being intratelluric followed by 
resorption, then resumed growth of the older crystals and crystalli¬ 
sation of the matrix, in this rock however under different conditions, 
so that the biotite crystals could not attain large dimensions. 
With the inverse proportion of alkalies and a high water content 
the conditions, when rapid cooling under pressure takes place, are 
favourable for the formation of analcime basalt or monehiquite; the 
large loss on ignition of the mineral here described makes the pre¬ 
sence of analcime in the matrix very probable. 
In the biotite leucite basalt (VII), containing but little MgO, which 
was described by Bucking from South Celebes the biotite occurs as 
resorbed phenocrysts and here also a second generation of small 
crystals occurs in the matrix; the crystallographically well defined 
phenocrysts of olivine have been altered completely into calcite and 
serpentine. In this case too the leucite is only found in the matrix, 
the larger crystals (0.1 m.m.) show feeble birefringence and vague twin¬ 
ning laminae. The apatite, which occurs here in fairly large quantities, 
is entirely absent in our rock. All the other East Indian leucite rocks 
are poor in biotite (Wichmann only mentions it in the tufas of the 
Peak of Maros) and in most of them leucite is not limited to the 
matrix (Djapara). 
Chemically the rock here described is distinguished from m 08 * 
other leucite basalts by its lamprophyric character. As in the case 
of the lamprophyric effusive minerals, separated into a distinct group 
by Rosenbusch and in which for instance the phlogopite bearing 
