124 Notices of Memoirs—The Geology of Porewpine. 
A very fine Heterangium from Shore was discovered by Mr. Lomax 
and his son in 1912. It is of large size, at least 17 mm. in diameter, 
though without secondary growth. The plant was originally 
compared with the so-called H. cylindricum, but is at least as close to 
H. tulieoides. The feature which at first seemed to be most striking 
is the fact that four distinct leaf-trace bundles enter the base of the 
leaf, each of them dividing into two in the petiole. This is certainly 
the best example yet found of a polydesmic petiole in Heterangium, 
and shows an interesting approach to the Medullosez in this respect. 
We may also compare Dr. Gordon’s new genus Rhetinangium. 
However, there is reason to believe that most of the British Coal- 
measure Heterangiums were polydesmic. In JZ. tilieoides there are 
four distinct bundles in the petiole, and the same was the case in 
H, Lomaxii. 
In all these plants two bundles start from the stele to form the 
leaf-trace, dividing into four, at least in some cases, before entering 
the leaf-base. Only in a very small stem from Dulesgate (not associated 
with H. Lomaxit) did a single bundle leave the stele (as in the 
Burntisland species), dividing into two on its outward course. This. 
little stem has nothing to connect it with any other form and may be 
distinguished as H. minimum. 
H1. tilieoides is maintained as a distinct species, mainly on the 
ground of its highly developed phloem with dilated medullary rays. 
In the behaviour of the leaf-traces it comes very near the Shore plant, 
which may, for the present at least, be kept distinct under the name 
HI. shorense. 
II.—Nore on tHe Guronogy or Porcuprne.! By J. B. Tyreext. 
HAVE been asked on two or three occasions whether I consider 
that the gold-bearing quartz veins in Porcupine are formed by 
the filling of fissures or by replacement of the rock in which they 
occur, and I have told individual members of an instance where 
bodies of quartz were undoubtedly introduced into similar pre- 
Cambrian rocks by metasomatic replacement, but some others among 
those present might be interested in hearing of the instance, so I will 
mention it. In the West Shining Tree country greenstones showing 
strongly marked ovoidal or pillow structure, similar to that so 
common in the amygdaloidal basalts of this district, are particularly 
abundant, and here and there through the greenstone quartz veins. 
occur, some of which have been determined to contain gold. The. 
individual ovoids or pillows are packed closely together, but there 
are angular portions of the greenstone in between them, and, as 
a rule, the rock inside the pillows and in the angular areas outside 
of them are almost precisely similar in character. In one place, 
however, the angular areas are entirely converted into quartz, which, 
as far as I could see, was precisely similar to the quartz in the veins. 
near by. As these angular areas had originally been greenstone, we 
have in them a clearly marked example of a metasomatic replacement. 
1 Extract from the Monthly Bulletin of the Canadian Mining Institute, 
June, 1915, pp. 397-8. 
