Dr. A. Wilmore—Uralite and other Amphiboles. 365 
contact with the augite. In another part he noticed that secondary 
hornblende, chlorite, and epidote have been developed very extensively 
along cleavages and cracks of the fresh plagioclase. 
The recent Survey memoir dealing with the north-west of Scotland? 
contains numerous references to the subject. It is shown that 
hornblende is sometimes compact and gives no evidence of secondary 
origin, but on the other hand much of the hornblende is evidently 
secondary after pyroxene. Some of the hornblende-felspar rocks of 
the Lewisian gneiss show hornblende with pyroxene cores (p. 62). 
The basic dykes and sills also show much secondary hornblende. The 
famous Scourie Dyke (wide ante) is quoted as an example. 
The presence of pyroxene cores in hornblende, the occurrence of 
needles of hornblende in the felspars (p. 93), the extension of the 
hornblende individuals parallel to the direction of shearing are 
observations similar to others already noted. Granulation of pyroxene 
is also noticed. 
The larger textbooks of mineralogy and petrology have, of course, 
devoted some space to a consideration of this subject. Zirkel, in his. 
Lehrbuch der Petrographie,* discusses ‘‘ Secundiire Amphibole”’ at some 
length. There is a good general summary of the chief observations 
followed by a discussion of the nature of the chemical changes. 
involved. One observation is worth reproduction. Schwerdt (Zeit. 
Geol. Ges., 1886, p. 225) records a case of Chiness diorite in which 
uralitization has commenced in the middle of the augite crystals so 
that green fibrous hornblende is seen to be surrounded by an envelope 
of compact augite. 
In the chemical discussion it is emphasized that the passage from 
pyroxene to amphibole is more than a mere paramorphism; it is 
a change of augite substance into hornblende substance. The analysis 
of the Ottawa uralite by Harrington is given (ede ante). This shows 
a loss of CaO of 9 per cent. and a gain of Mg O of 33 per cent. There 
is an increase of both ferrous and ferric oxides. There is also an 
analysis of a uralite derived from the pyroxene of a gabbro from 
Zwartekoppies (Dahms). This shows a gain of CaO of 6 per cent., 
a loss of Mg O of 6 per cent., and a gain of Fe O of 3 per cent. These 
results are obviously quite contradictory, but it is pointed out that the 
first case concerns a basic rock rich in lime (24°44 per cent.), while 
the second deals with a rock poor in lime and rich in magnesia and 
iron oxides. 
The deposit of needles and microliths of hornblende in the felspars. 
of many rocks—the so-called erratic (gewanderte) hornblende — 
receives fairly full treatment, and there is a series of references. 
Quite recently MM. L. Dupare & T. H. Hornung*® have made 
a most interesting contribution to the literature of this subject. Their 
paper is entitled ‘‘Sur une novelle théorie de Pcuralitisation”’. They 
describe the alteration noticed in a fine series of rocks collected in the 
Northern Urals. These rocks are very ‘fresh’ and are made up of 
1 « The Geological Structure of the North-West Highlands of Scotland ’’?: Mem. 
Geol. Sury. Great Britain, 1907. 
* 1893, vol. i, p. 316 et seq. 
3 C.R. Acad. Sci. Paris, vol. cxxxix. 
