Dawkins—-Rhetic Beds. 259 
beds of the Lower Lias, its fossils, so far as they had at that time 
been made out, being as much Liassic as Rheetic; for if Monotis 
decussata, Cardium Rheticum, Pleurophorus (sp.), and Ostrea inter- 
striata bound it to the latter formation, so also did Modiola Hillana, 
Pecten textorius, Pholadomya glabra, and Lima punctata bind it to 
theformer. In the conflicting paleontological evidence, therefore, as 
to true classification, I appealed to its lithology; and, as it contrasts 
strongly with the beds below in the absence of arenaceous deposits, 
and was akin to those above in the large development of the calca- 
reous element, I classed it with the latter. Since that time, how- 
ever, additional paleontological evidence has been adduced, that 
turns the scale the other way. Mr. R. Tate, F.G.S., in a list of 
fossils from the White Lias of the neighbourhood of Belfast (Quart. 
Journ. Geol. Soc. vol. xx. p. 109), adds to its fauna Aainws cloa- 
cinus, Quensted, A. concentricus(?), Moore,and an Arca closely allied 
to A. Lycetti, all of which, up to that time, had been found only in 
the Avicula-contorta-series below. It is therefore evident, that, 
while these beds, by the presence of a mixed molluscan fauna are 
passage-beds, they are more akin to the Rhetic formation than to 
the Liassic; the lithological characteristics derived from varying 
depth of sea, proximity to land, and the like, being of far less value 
in classification than the evidence afforded by paleontology. It is 
for this reason, therefore, that I consider the White Lias to consti- 
tute the Upper Rhetic group. The great breaks in the succes- 
sion of life, both above and below, prove that great intervals 
elapsed between the deposition of the Avicula-contorta-series, below, 
and the White Lias, as also between the latter and the Ammonites- 
planorbis-zone. 
Il. Avicula-contorta-group, or Middle Rhetic.—This is com- 
posed of a series of dark and grey marls, thinly bedded, micaceous, 
and pyritous sandstones, and dark-grey or blue limestones. Some- 
times there is a layer of conglomerate, as in a section near Frome, 
described by Mr. C. Moore, F.G.S. (Quart. Journ. Geol. Soc., vol. 
xvii. p.497). Very generally the beds are charged with a fibrous 
carbonate of lime, strongly resembling gypsum, and are more or less 
micaceous. Throughout the series, traces of animal life are remark- 
ably abundant; and usually at the base there is a Bone-bed, made 
up of the remains of Fishes and Saurians, and more or less conglo- 
meratic. This bed, at Diegerloch, near Stuttgart, yielded teeth of 
Microlestes to Professor Plieninger. From this also, or from the 
dark shale above, which contains similar organic remains, the mam- 
malian teeth found by the industry of Mr. C. Moore, in a fissure of 
the Carboniferous Limestone, near Frome, were probably derived, 
the stratum in which they were originally deposited having been 
broken up and washed into the fissure, together with the débris of 
other and younger rocks. 
Besides the Bone-bed universally present at the base of the Avi- 
cula-contorta-series, there are two more, on the Watchet shore, in 
the middle and upper parts. Two or three beds of dark impure 
limestone, charged with fibrous carbonate of lime, and composed in 
