226 Dr. G. J. Hinde—Spicules in Archeocyathus. 
black crystals, which must have consolidated almost at the same time 
as the granular ground-mass. The structure of the rock seems not 
incompatible with the idea that it was formed in the pipe of a dying — 
volcano, when the upward flow became gradually arrested and the 
remaining magma slowly solidified into a plug under the pressure of 
the superincumbent column. ‘Tourmaline, though not a constituent 
of true lavas, is by no means unknown in the quartz-porphyries of 
some other districts: the blue variety occurs, for instance, in the 
Harz Mountains. __ > 
P.S.—With reference to the discovery of glaucophane in Anglesey, 
announced by Prof. Blake in the March Number of this Macazinu, 
it may be noted that the blue amphibole of the Mynydd Mawr rock 
differs from that mineral in the character of its absorption and 
pleochroism, as well as in the absence of crystal form and of the 
peculiar “cross-jointing.” Glaucophane has not, I believe, been 
recorded from non-metamorphic igneous rocks. <A good résumé of 
the literature relating to this mineral has recently been given by 
Oebbeke.! 
V.—NOoTE ON THE SPICULES DESCRIBED BY BILLINGS IN CONNECTION 
WITH THE STRUCTURE OF ARCH ZOCY4aTHUS MINGANENSIS. 
By Grorcre Jennines Hinpe, Ph.D., F.G.S. 
N “The Palzozoic Fossils of Canada,” vol. i. p. 8, the late 
| Mr. Billings stated that by treating a silicified specimen of 
Archeocyathus Minganensis with acid, he ascertained that it contained 
numerous siliceous spicula—slender, fusiform, slightly curved, acute 
at both extremities—and that these fossils must therefore be 
classified among the extinct tribes of sponges. Referring again to 
this species in the latter part of the same volume (pp. 854-357), 
this author states that he had found the same spicula present in great 
numbers in another large species, Trichospongia sericea, and that it 
therefore remained an open question whether they actually form 
part of the structure of Archeocyathus, or belonged to Trichospongia. 
In addition, however, to these simple detached spicules, Mr. Billings 
describes and figures (loc. cit. p. 355, fig. 844) “ branching spicula,” 
which ‘are seen imbedded in, and forming a part of, the substance 
of the outer wall of A. Minganensis.” No doubt could be enter- 
tained that these so-termed branching spicula really belonged to the 
fossil, since they could “ be seen, not only projecting from the surface 
of the silicified specimens, but also in the thin slices prepared for 
the microscope.” 
Since the description of Archeocyathus by Mr. Billings appeared, 
the nature of this fossil has been investigated and referred to by 
several eminent paleontologists, amongst whom may be mentioned, 
1 See Ueber den Glaukophan und seine Verbreitung in Gesteinen, von Herrn K. 
Oebbeke, Zeitsch. der deutschen Geologischen Gesellschaft, 1886, vol. 38, p. 634. 
