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Devonian rocks and in those of the Carboniferous, Liassic, 
Oolitic, Purbeck, and Wealden. Nevertheless he is of opinion 
that “ Although occurring so constantly in the different geolvical 
periods from the Devonian to the Wealden, and again in recent 
marine and fresh waters, yet it is in the Triassic deposits of 
England and the Continent, and in the plant-bearing beds of 
Virginia and Central India, that this little bivalved Entomostracan 
appears to be pre-eminently abundant, so as to serve probably 
as a faithful index of a peculiar geological horizon.” 
To the Estheria-bed, succeed about four feet of Clayey Shales, 
which are followed by the bed known as the Monotis-bed. This 
is one of the most remarkable in the district for the number of 
shells it contains of this species, in a beautiful state of preser- 
vation, with an occasional Modiola minima intermixed. The 
prevailing fossil on the under side of the slabs on which Menotis 
is found, is a Myacites, which much resembles, if it be not 
identical with Myacites liassinus of Quenstedt, and is interesting 
as being the first of that genus and family subsequently so 
extensively developed throughout the Jurassic period. Monotis 
seems properly to be considered a sub-genus of 4Avicula, differing 
no more from the species with prolonged bases or binge-lines, 
which subsequently take its place, than do the Meleagrine from 
the Avieule of the present time. Considered then as an Avicula 
it is a form which is known to us in the “ Caradoc” and probably 
lower still. 
From a consideration of the foregoing circumstances it will 
be seen that in connexion with mineralogical characters entirely 
liassic, we have a zone of life which as certainly appears to have 
its affinites with the preceding period. How far it may be wholly 
assignable to the “Trias” as has been done by some competent 
geologists, may perhaps still admit of question. Many regard 
the entire zone, comprising on the Continent of Europe a 
succession of beds not less than 200 feet in thickness, as repre- 
senting a truly transitionary period, and as such entitled to a 
separate and distinct rank, having analogies with both the 
contiguous formations, yet strictly assignable to neither. Here 
at any rate is a field for study and observation which can only be 
successfully worked out by a careful comparison of the series of 
beds as displayed in our own county at Westbury, Wainlode, 
Aust, &c., with the same beds at Binton and other localities in 
Warwickshire, at Penarth near Cardiff, at Axmouth in Devon- 
shire, and wherever else they may be exposed in the British 
Islands ; and these again must be correlated with those on the 
Continent of Europe, where a more extensive development 
illustrated by a far larger series of fossil remains, will no doubt 
eventually enable geologists to determine with exactitude and 
correctness, the true value of the beds in the geological scale. 
With reference to the upper beds of the “ New Red,” and in 
