260 Dawkins — Rhetic Beds. 
great part of crushed Pecten Valoniensis, Defrance, appearing at Up- 
hill, Watchet, and Stoke-Courcy, characterize the upper portion of 
the series. The fact, that the pebbles included in the conglomeratic 
bone-bed at the base are rounded fragments of the subjacent rock, 
intimates an interval of greater or less length, during which the 
subjacent sands became indurated into sandstone, and so elevated as 
to be exposed to the violence of the waves. Quartzose pebbles also 
prove that the Mid-Rhatic sea beat against cliffs of Devonian age. 
In thickness the Avicula-contorta-series varies from eleven feet, at 
Beer-Crowcombe, to twenty-tive feet at Saltford. Its sandstones, 
shales, and earthy limestones prove it to have been deposited in 
comparatively shallow water, and not very far from land. 
IV. The Lower Rhetic Marls and Marlstones—These are gene- 
rally unfossiliferous; and, from their conformity with, and gradual 
passage into the Red Marls of the Keuper, were formerly considered 
to belong to the latter. The Marlstones are hard, grey, and slightly 
calcareous; and are at some places intercalated with a coal-black 
shale, as on the Watchet shore. The upper Marlstones are laminated, 
ripple-marked, and traversed by the borings of Annelids. Some- 
times both marls and marlstones are highly gypseous. I have in- 
cluded both in the Rhztic Formation on the evidence of the fossils 
found some 10 feet below the Bone-bed to the west of Watchet. 
They consist of Modiola minima, Myacites striato-granulata, Ger- 
villia precursor, Pecten Valoniensis, Pullastra arenicola, Cardium 
Rheticum, Saurichthys apicalis, Gyrolepis Alberti, G. tenuistriatus, 
Acrodus minimus, and Sargodon Tomicus, besides many forms too 
fragmentary to be identified. Here I obtained also a tooth of the 
oldest British mammal yet found in a stratified deposit. It is allied 
to the Kangaroo-rat, and is described in the paper before alluded to, 
under the provisional name of Hypsiprymnopsis Rheticus. This 
assemblage of species proves beyond all doubt the Rhetic age of the 
rocks in which they occur; and, as the latter differ in no respect 
from the grey unfossiliferous marls and marlstones lying beneath, save 
in the accidental preservation of the fossils, it is a fair inference that 
both fossiliferous and unfossiliferous belong to the same group. 
Lithologically, in colour and texture, and in the arenaceous condi- 
tions of deposit, they are identical. Considering, therefore, the 
preservation or non-preservation of the fossils a mere accident, I 
propose to include the grey marls, marlstones, and black shales, 
down to the point where the Red Marls begin to appear, in the 
Rhetie Formation, whether they be fossiliferous or not. The thick- 
ness of the rocks so defined, from the Bone-bed above downwards 
to the first layer of Red Marl, on the east side of Watchet harbour, 
is 58 feet, and at Saltford 30 feet. Further down, beneath alterna- 
tions of Red and Grey Marls and Marlstones, that prove the gra- 
dual passage of the Keuper into the Lower Rheetic series, is the 
deep-red marl so characteristic of the former, 
A tabular list of Rheetic fossils is given at p. 406 of the paper 
alluded to above. 
