360 _REPORT—1846. 
We are unable to conjecture why the latter formula should have been pre- 
ferred to the former, unless because the combination Al, Si was supposed 
improbable; examples however of such a combination are afforded by Kolly- 
rite Als Si+15H, Heterokline Mn’ $i, and Sismondine 4Fe? Si+5AP Si 
+15H. 
We may also call attention to the fact, that the slag in question has the 
same hardness as natural Gehlenite. 
Admitting this slag to be really Gehlenite, the: circumstance of its pro- 
duction at a high temperature in an iron furnace, may possibly be made 
available by the geologist in explaining the formation of the rocks in which 
the natural mineral occurs in Fassathal in the Tyrol. We subjoin in a note 
the following interesting description of the locality of Gehlenite by Von 
Buch, translated by Mr. Warington Smyth, of the Museum of Economic 
Geology *. 
8. 
This specimen was also presented to us by Mr. Dawes. It was obtained 
during the process of remelting cast iron with lime in a small cupola. 
No. 8 is a mass of pearl-gray slag containing imbedded long yellow erystals 
which appear to be square prisms with the angles truncated, cleavable per- 
pendicular to the axis of the prism. In part of the specimen the crystals 
are very fine and radiated. 
8. Anatysis. By D. F. 
Nitrous acid was employed, instead of hydrochloric, to decompose this 
slag. Magnesia and potass were not present. After the precipitation of the 
* The syenite of Mount Monzon descends steeply from the snow limit, and is very like 
the zircon syenite of Norway. The hornblende is green, and accompanied by grains of 
iron pyrites. Tourmaline also appears there in crystals, radiating from a centre. In cracks 
and hollows of this syenite are found Vesuvian, Gehlenite, brown garnet, Ceylanite and 
Fassaite, a sort of augite. 
In ascending the branch valley from Vigo to Monzon (see plan) fine cliffs of dolomite are 
seen on both sides, and on the left the augitic porphyry, or melaphyre, is seen to underlie 
it; higher up the whole valley is strewed with blocks of syenite fallen from the Alp above. 
From beneath the height may be seen a thick bed of Vesuvian, from which fragments 
often fall, though no one has as yet been able to ascend to it; its crystals are four-sided 
prisms with the terminal faces much-modified, and are always imbedded in cale spar, gene- 
rally of a blue colour. 
Cordier considered that the Gehlenite is only Vesuvian with its crystallization impeded by 
the presence of cale spar. There are also brown crystals enveloped in cale spar, with 
neither end free, and these are undistinguishable from Vesuvian. When they form groups 
together, they lose lustre and colour, and the calc spar disappears. The only place where 
it is found is quite on the west side of the syenite, close to the dolomite; for it is only near 
the edges that calc spar, which always accompanies these foreign minerals, is found in the 
syenite. 
Above the Vesuvian and Gehlenite are fine druses of Ceylanite in crowded and generally 
good dark octohedrons; which were probably at first also imbedded in cale spar, since a 
little of it, with corroded surface, sometimes lies among the crystals. In a similar manner 
the sort of augite termed Fassaite lies in calc spar; when fresh the crystals are fine grass- 
green: this augite is often found on the sides of Vesuvian crystals. 
At Monzon the cracks are often covered with fine rhombohedrons of chabasite, and some- 
times are slight traces of mesotype, the only zoolites found here; though among the other 
zoolites in the Fassa valley chabasite is not found. 
The relations of this syenite to the red sandstone and to the porphyry are difficult to 
determine, from the great steepness of the mountain on the south side also. 
