Geological Society of London. 101 
tutes a well-defined basin of an elongated oval shape, the 
great axis of which is directed nearly N.E. and S.W., and has 
a length of about 20 German geographical miles, with a maxi- 
mum breadth of 10. Itis from 55 to 60 miles in circumference. 
Towards the N.E. and N. a small portion is bounded by the 
Trias, the Quader-sandstone, the Planer-kalk, or by the Carbo- 
niferous formation. Elsewhere, for two-thirds of its margin, 
granite or primordial crystalline rocks, such as gneiss and 
mica-slate, constitute its base and its boundary. A few small 
carboniferous basins are sprinkled over the Silurian surface, 
as well as a few isolated outliers of cretaceous beds. The 
dip in the two halves of the basin, the one to the N.E. and 
the other to the S.E. of the chief diameter, is towards the 
principal axis. The beds ordinarily lie at an angle of from 
30° to 45°, often 70°, and are not unfrequently vertical. 
M. Barrande distinguishes eight stages of strata to which 
he assigns a Silurian age; four of them he regards as Lower 
Silurian, and four as Upper Silurian. Of his Lower Silurian 
Stages the two lowermost are azoic, the distinctions between 
them being founded on mineral characters, the first being 
composed of crystalline rocks, and the second of clay-slates 
and conglomerates, similar to the fossiliferous Silurian above 
them, but wholly void of organic remains. They are rich in 
lead mines. These azoic stages pass into each other, and the 
upper section passes gradually into the fossiliferous beds 
above. ; ‘4 
‘The third stage of his Lower Silurian, and the first of his 
fossiliferous horizons, includes his ‘“ Schiste protozoique,” 
and attains a thickness of 1200 feet. It contains no beds 
of limestone. The fauna of this section is very peculiar; it 
is composed almost totally of Trilobites, the other fossils 
being a Pteropod, some Cystidez, and an Orthis. These 
constitute an assemblage upon which he lays great stress, 
and designates primordial. All its species, without exception, 
are peculiar to itself, and of the Trilobites, all the genera 
are so, with the exception of Agnostus. The peculiar genera 
are either low and rudimentary types, or members of the 
Olenoid or Calymenoid families ; not typical or highly de- 
veloped forms. They are Paradowides, Conocephalus, El- 
