562 REPORT—1904. 
It is well known that crystallisation may result in a concentration of material, 
as when the small crystals in a solution become redissolved and reappear as a large 
crystal, That the concentrating agency in the case of the decomposed pyrites may 
have been crystallisation is suggested by the fact that the nucleus has crystal 
facets. 
Other examples of the attractive force exerted during the growth of crystals are 
afforded by such things as gypsum growing in clay, where, as was pointed out by 
Bunsen, the force does work and thrusts up the clay, often in considerable masses. 
Again, Klocke found that an alum crystal during growth may raise itself in the 
solution. 
If this attractive force exists it should also manifest itself in a concentration of 
the material in the neighbourhood of a growing crystal, and this the author has 
found to be the case. By means of total internal reflection he has determined the 
index of refraction, and hence the composition, of the solution in contact with 
growing crystals of alum and other substances, aud has always found the solution 
to be supersaturated. 
The author suggests that in cases where no other explanation is forthcoming a 
sufficient cause for concretionary growth may be found in the attractive action of 
growing crystals. Marcasite, hematite, barytes, and many other concretions, are 
really crystalline in structure; and Liversidge has shown that gold nuggets are 
always so. 
6. Basic Patches in the Granite of Mount Sorrel, Leicestershire. 
By R. H. Rasrart, B.A. 
Dark-coloured patches are very abundant, and may be divided into three 
types :— 
(1) Small black or grey angular patches, without porphyritie felspars. 
(2) Larger ovoid patches of a brown colour, with pink porphyritic felspars, 
(3) Black patches showing banding and Jit-par-lit injection by the granite. 
Type (1) consists of felspars and hornblende with a little quartz. Small 
erystals of plagioclase and hornblende are enclosed in poecilitic fashion by large 
plates of orthoclase. 
The second type is very similar microscopically, but quartz is more abundant, 
The large felspars are often much corroded. 
Both types are almost free from biotite, although in the normal granite it 
is the dominant melanocratic mineral. There is abundant sphene, of a peculiar 
habit, often moulded on the felspars, with an approach to ophitic structure. 
These patches show a great resemblance to many metamorphosed basic igneous 
rocks, and attention is called to the resemblance between them and the early 
stages of the alteration of the Scourie Dyke, described by Mr. Teall.’ It is con- 
cluded that they are fragments of basic rocks caught up by the granite magma 
during intrusion. 
A specimen of the banded type consists of brown biotite and magnetite, 
enclosed poecilitically by plates of perthite, microcline, or orthoclase, It is very 
like many metamorphosed slates, and is probably a fragment of a sedimentary 
rock, This type is rare. 
7. On the Different Modifications of Zircon. 
By L. J. Spencer, M.A. 
Some very irregularly developed crystals of zircon from the gem-washings of 
the Balangoda district in Ceylon were found to have characters differing widely 
from those of zircons of more common occurrence. Although of low specific 
gravity (4:0), they are not increased in density when strongly ignited, as are many 
1 0.I.GS., 1885, p. 133. 
