TRANSACTIONS OF THE SECTIONS. 69 
are often separated by several hundred feet of barren strata, is one of the chief rea- 
sons why a Cambrian fauna has not been discovered before. 
The fossils already discovered in this bed include a new genus, Plutonia, with 
species of Paradoxides, Microdiscus, Conocoryphe, Agnostus, Theca, Discina, Obolella, 
and Lingulella; the shells seem much like species in the “ Menevian group,” and 
are probably identical ; but the Trilobites are all new species, and the new genus, 
for which the author proposes the name Plutonia, is only known to occur in these beds. 
This remarkable fossil is of very large size, equalling, indeed, in this respect Paradox- 
ides Davidis, It is perhaps also more nearly allied to the genus Paradovides than 
to any other known, but its peculiar character of being covered all over with very 
strong tubercles, associated with an unusual position for the eye suture, and straight, 
very long thoracic pleurz, is sufficient to stamp it a new and distinct genus. 
Resting upon the yellowish-grey rocks in which this richly fossiliferous bed 
occurs, is another series of purple and red sandstones, also slightly fessiliferous ; 
and these directly underlie the grey beds of the ‘“ Menevian group,” which con- 
tain Paradoxides Aurora and other fossils. Mr. Salter and the author have at dif- 
ferent times proposed, in consequence of the lithological resemblance of the lower or 
Paradoxides Aurora beds of the “ Menevian group” to some of the beds of the “ Har- 
lech group,” to have the “ Menevian”’ included in the Lower Cambrian. This 
now seems to the author more than ever necessary, and on paleontological grounds ; 
for the genera, so far discovered, are either identical or very nearly allied ; and some 
of the species are the same in both groups. On the other hand, there is very 
little connexion palwontologically between the “ Menevian group” and the over- 
lying “Ffestiniog group.” No representatives of the more remarkable ‘“ Mene- 
vian” genera appear there; Paradoxides, Microdiscus, Erinnys, &c. are entirely 
absent, the very far-ranging genera Aynostus and Conocoryphe seeming alone of 
the Crustacea to reach upwards. Even with our present knowledge, therefore, 
of the two faunas “Harlech” and “ Menevian,” an unusually close connexion 
must be allowed to exist between them; and doubtless the more we know of 
the two, the more intimate will this yet seem, and the more shall we see the 
necessity of uniting both in the same geological division. To separate two such 
groups even into Upper and Lower Cambrian seems scarcely possible or reason- 
able; but to attempt to have a boundary for the great formations “ Silurian” 
and “Cambrian” in the very heart of a period where such marked evidences 
of similarity in the life which ranged through them occur, would only prove 
once more the fallacy of artificial divisions instituted on purely litholcegical grounds 
instead of on evidence based on paleontological facts. If the “Menevian group” 
be included along with the “ Harlech group” in the ‘‘ Lower Cambrian” of Pro- 
fessor Sedewick or “‘ Cambrian” of Sir R. Murchison, we shall have a well-marked 
upper boundary to the formation defined by such genera as Paradowides, Micro- 
discus, Anopolenus, Erinnys, and other allied forms; and as these are altogether so 
very distinct from any yet found in the higher groups, this limit is not at all likely 
te be disturbed by any future discoveries. 
On the Ferruginous Sandstone of the Neighbourhood of Northampton. 
By Cuarxes JECKS. 
Having devoted some attention to the ferruginous sandstone of the Lower Oolite 
in the immediate neighbourhood of Northampton, the author suggested the follow- 
ing as the mode of its formation. Let the existence of a wide estuary be supposed, 
into which mighty rivers discharge themselves, depositing therein quantities of 
sand, mud, &c.; at times it may happen that one or more of the rivers above 
referred to may, perhaps, in periods of unusual outflow, bring down and deposit in 
the estuary a certain amount of iron; let then a subsidence be supposed, followed 
by the deposition of those shells inhabiting deeper water, and also accompanied 
by the formation of what is called ironstone. Then after a long period of time 
let there be a gradual upheaval, and as the submerged land approaches the sur- 
face, again an outpouring of iron, accompanied by the deposition of those shells 
inhabiting shallower water, drift-wood, &c.; and let this be continued for, it may 
be, many hundreds, perhaps thousands of years, together with fresh depositions of 
