Murchison’s Siluria. 379 
- Both Barrande and Murchison agree in considering the “ Pri- 
mordial F'auna” to be represented in Great Britain, although not 
as sharply limited as in Bohemia, by the so-called Lingula beds 
of Wales, which contain Paradoxides, Conocephalus, Agnostus, 
and Lingula, and by certain beds in the Malvern Hills, contain- 
ing Olenus. The same genera are typical of the lowest band 
containing organic life in Scandinavia, where the Azoic rocks are 
developed over an immense space and everywhere recognised as 
unconformable with the fossiliferous strata. The number of 
Species of trilobites in the Primordial Fauna of this region is very 
great, but they have not yet been as thoroughly studied as those of 
Bohemia, ‘T'he lowest zone of organic life, however, is occupied 
by fucoids only. 
In this country we recognise the existence of the Azoic System 
over an immense extent of teritory in the Northwest. The fact 
that the Lower Silurian sandstones rest upon the upturned edges 
testing one.* In the Azoic rocks we have slates, ripple-marked 
quartz rocks, and occasionally thin bands of limestone with inter- 
Stratified traps in immense masses, the whole being so: olded over 
} and metamorphosed as to render any estimate of their entire thick- 
hess but little better than a mere guess. ‘T'hese rocks extend far to 
| the Northwest, but are much covered by heavy accumulations of 
| drift, and, being in an almost uninhabited country, have been but 
little explored in their details. In Missouri, the oldest fossiliferous 
petior the few relics of organic existence which have been found 
have a marked analogy with what has elsewhere been observed 
in the oldest fossilifeous rocks. The only trilobite thus far ob- 
Served is a Paradorides or a closely allied genus; besides. there 
ate a few fucoids and Lingula. Farther west, however, in the 
Same sandstone, on the St. Croix river, a series of trilobite beds, 
lying at the base of the fossiliferous formations, has been discov- 
ered by Dr. D. D. Owen, in the drawings of which Barrande has 
recognised forms either identical with or in the highest degree 
tesembling Paradovides, but of which the fragments figured in 
* Marchison has been, in several instances, led into 
es, led in great erors by adopting e- 
Jules Marcou as one of his American authorities, ° Thus he has failed to recognise the 
bi ower Silurian enc . Azoic in the Northwest, a well-estab- 
| “‘Mneonformability of the Lower Silurian and the Azoic ofp i oa mag 
