148 The American GeoUxjisf. March, 1895 
round in tlu- shales ol' the Etcheuiiiiian series, sonic from a 
thousand feet below the EUipsocephalus horizon, above re- 
ferred to. The predominance of organisms of low organization 
thus appears to be a notable mark of faunas at the base of the 
Cambrian. 
In giving a sketch of Mr. Cayeux's work on the Protozoa of 
the pre-Cambrian of Brittany, I take up first his later paper 
(June, 1894) describing the Foraminifera which he found with 
radiolarians (the latter being by far the most numerous) and 
which he says "r)riginally had a calcareous shell." 
This fauna was found in the siliceous rocks on the north of 
Brittany, known under the name of "phtanites" and placed at 
the border of the crystalline schists and the clay slates (or 
"schists") of Saint Lo. 
Mode of orciirrenre of the Had iola rio iix aitd Fora iii un'fera. 
"Hati}^ lias formed the name 7>///rr////'e for siliceous strafiped 
rocks, disposed in thin beds, frequently repeated and of great 
extent in the ('ambrian and Silurian formations.* A certain 
number of the beds in Brittan}' are true phtanites, in the mod- 
ern petrographical sense of the word ; but the greater part 
present their silica entirely crystallized to the condition of 
quartz and should be classed as quartzite." 
Dr. Charles Barrois, who first discovered traces of railiola- 
rians in the rocks of Brittany, and placed them in the hands 
of Mr. ( Jayeux for study, has carefully worked out the geolog- 
ical horizon of the phtanites, and finds that the}" have given 
pebbles to the conglomerates at the base of the Cambrian and 
to those of the schists of Saint Lo, and, therefore, must be as 
low as the base of the latter. He has asserted that these 
schists are identical with the Uriconian of ('aer Caradoc, and 
are non-metamorphic representatives of the Peliidian of St. 
David's in Wales. Dr. Barrois also has traced these phtanites 
and quartzites throughout lirittany, but has found their asso- 
ciations greatl}^ changed in some parts, viz. : 
1. They are contained in granulitic gneiss at Varmes. 
2. In mica-schists and micaceous schists at Lorient, St Na- 
zaire and Nantes. 
*T]iis term ai)pcars to corresi)oii(l lo Ihc '■clicri."" '■siliciMnis slates." 
or siliceous mud rocks, of early Eiij^lisli aulluirs. perliai's the most sili- 
ceous of Ihem. 
