PRESIDENT’S ADDRESS. 345 
but in Northern Brittany it occurs near the base of the series of 
Saint-L6 ; as is proved not only by stratigraphical evidence, but 
by the occurrence of pebbles of the easily recognised gyaphitic rock 
in conglomerates at Granville and other places which are them- 
selves low down in the series. So that the horizon of these fossils 
seems to be somewhere near the middle of the pre-Cambrian sedi- 
mentary rocks of Brittany. Whether these rocks belong to the 
Huronian or to the Algonkian, or partly to one and partly to the 
other, there is no certain evidence ; but as they agree in mineral 
structure more closely with those of the Huronian of Canada than 
with those of the Algonkian, and as they contain numerous scales 
of graphite, they may be placed provisionally in the former period. 
Dr. Cayeux’s specimens have been examined by Dr. D. Rust, 
and by Dr. G. J. Hinde, both highly competent authorities. Dr. 
Riist, while allowing that they are organic, is inclined to think, 
from their small size and spherical shape, that they may be 
detached chambers of Foraminifera ; but Dr. Hinde upholds 
Dr. Cayeux’s view that they are truly Radiolarians* ; and if we 
may rely upon the published figures, photographs of which I 
exhibit—and no one has thrown any doubt on them—they cer- 
tainly appear to be Radiolarians and sponge-spicules. The figures 
of the Foraminifera seem more doubtful ; but as they are described 
as having finely perforated walls we cannot escape from the con- 
clusion that they are true Foraminifera, and distinct from the 
Radiolarians which have coarsely perforated walls. The Foram- 
inifera, however, are few, and consist of groups of simple spherules 
of different sizes which sometimes possess the rudiments of spines. 
The Radiolarians are very minute, about one-fifteenth of the 
diameter of similar forms in Cambrian and younger rocks. Most 
of them have a thin spherical shell pierced with holes, and are 
sometimes furnished with spines; but the forms are various. 
Twenty-four genera have been distinguished, two-thirds of which 
are still living, and there are many others, the genus of which 
cannot be determined, although they are unquestionably Radio- 
larians. By far the commonest forms belong to Cerosphera, a 
still living genus, known also in the Silurian period, which belongs 
to the legion Spumellaria, the fundamental form of which is 
spherical or ellipsoid. But the legion Nassellaria, in which the 
fundamental form is ovoid, is also represented by nine genera, 
although the individuals are not so numerous as those of the first 
legion. 
Sponge-spicules are probably common, but they are generally 
broken. They belong chiefly to the simple forms of Monactinel- 
lide, or to the Lithistide, or the Tetractinellide ; but a few frag- 
ments belonging to the Hexactinellide have been recognised. 
* Geological Magazine, 1894, p. 417. 
