448 PROFESSOR HEDDLE ON 
merely a trace of magnetite. In this last case even inspection with the micro- 
scope did not suffice to disclose its nature. 
Granting that most “black sands” are mixtures of true iserine with mag- 
netite, the magnet does not suffice for their separation, for I have found that 
the more titaniferous portion is occasionally the more powerfully magnetic of 
the two; though this may be the result of a partial change of the magnetite 
into martite. With the exception of those from Elie and from St. Andrews, 
I regard all the samples analysed by me, as being probably mixtures. 
1. Is found in very minute magnetic black grains in the sand of the shore, 
a little to the north of the Manse of Hoy, Orkney. A considerable quantity 
of black sand may be gathered, very little of which is magnetic. There is no 
appearance of the mineral in the flaggy rock of the neighbourhood, and as 
igneous rocks lie about a mile to the west, these probably were its matrix. 
The magnetic portion yielded— 
Titanic Acid, 5 . : : : 18°4 
Alumina, . ; ; ; ‘ ; °6 
Ferric Oxide, ; . : . : 54:979 
Ferrous Oxide, . : F 5 ; 14°422 
Lime, . , ; é ‘ : 5°6 
Magnesia, . : ; . : ‘ "2 
Silica, . ; : : : : : bal 
100°301 
It appeared as very minute black grains, which differed considerably from 
ordinary granular iserine. When examined with the microscope they were 
found to consist almost entirely of oval grains with rounded outline. They 
shine like little bits of graphite ; have few fractures, which are highly lustrous. 
There was very rarely a doubtful outline of a worn octahedron. The non- 
magnetic, or very feebly magnetic portion of this black sand, was, under the 
microscope, quite similar to the magnetic portion. That portion may have 
passed into martite. 
2. Was found in very considerable quantity on the surface of a quicksand, 
on the west shore of the lake at Sandwood, on the west coast of Sutherland. 
The Torridon sandstone forms the south shore of this lake, and the 
Hebridian gneiss, the greater part of its northern shore. The black sand 
probably came from the last named rock. 
