364. Dr. A. Wilmore—Uralite and other Amphiboles. 
and a gain of magnesia. (This change is, however, far from constant. 
See, e.g., Teall on the Scourie Dyke.) 
It was further pointed out that the schistose structure of the rocks 
is largely due to the production of fibrous hornblende. This secondary 
fibrous hornblende does not remain in the area formerly occupied 
by the pyroxene; amphibole needles are even found along the 
cleavage cracks of the felspars. Some other points from this important 
memoir are— 
(1) Brown hornblende passes into green hornblende by the reduction of its 
iron from the ferric to the ferrous state ; afterwards loss of iron produces 
fibrous and less coloured hornblende. 
(2) Very often there is a double hornblende zone round a pyroxene core ; first 
Ces brown and more compact hornblende, then green and more fibrous 
hornblende. 
Another important United States monograph is that of F. D. Chester. 
He distinguished between tremolite and fibrous green hornblende in 
his remarks on rocks at Iron Hill. Tremolite is evidently regarded 
as colourless or nearly so. Fibrous green hornblende surrounds 
hypersthene cores, and tremolite fibres are developed irregularly 
within the core. Much magnetite is set free as the result of the 
change, which Chester described as a paramorphic one. 
It is pointed out that ‘ uralite’ is used in an ambiguous way— 
(1) To indicate a substance with the external form of augite, but the cleavage 
and optical properties of hornblende. 
(2) Fibrous hornblende is loosely described as uralite. 
The three papers by W. 8. Bayley on the Basic Massive Rocks of 
the Lake Superior Region necessarily contain several references to 
uralite and uralitization.* The first of these papers gives an interesting 
history of the classification of the gabbros from the time of Hauy. 
The third article contains an account of the different structure-planes 
noticeable in some of the augites. Diallage cleavages are accentuated 
by dark decomposition products, the most abundant of which are tiny 
irregular black and brown dots. These are scattered everywhere 
throughout the pyroxenes, but are accumulated most thickly in the 
neighbourhood of the cleavage lines. Peculiar platy inclusions 
characteristic of gabbro-diallage are seen in some of the pyroxenes. 
These are often arranged in straight lines crossing the parting-planes. 
They are frequently so crowded that the line of inclusions appears 
as a dark bar crossing the diallage at various inclinations to the 
cleavage. 
In 1888 A. C. Lawson, of the Canadian Survey, made some con- 
tributions to our knowledge of the subject. In a chapter on the 
Petrography of the Keewatin Series he pointed out that the pyroxene 
of rocks of the gabbro type is more resistant to ‘ paramorphie change’ 
than the augite of the diabases. Shreds of fibrous hornblende or 
actinolite derived from augite are observed to have been developed 
within the substance of the fresh plagioclase, and along its line of 
oe “‘ The Gabbros and Associated Rocks in Delaware’’: Bull. U.S.G.S., 1890, 
0. d9. 
* Amer. Journ. Sci., 1893, vol. i, pp. 433, 587, 688. 
3 Report on the Geology of the Rainy Lake Region: Geol. and Nat. Hist. Surv. 
of Canada, Montreal, 1888. 
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