THE EH^TIC KOCKS OP NOTTINGHAMSHIRE. 
199 
The Upper Rhsetic marls were not seen in situ, but limestone 
nodules with Estheriee were found in the overlying drift. 
Now, as I have already said, I cannot admit that the green marls 
which in this and the adjoining districts come below the Avicula 
contorta shales belong to the Khsetic series ; for whilst there is always 
a sharp stratigraphical line of division, with, in some cases, evidences 
of erosion, between the green marls and the paper shales there is 
every appearance of a passage between these green marls and the under¬ 
lying red and green marls of the Upper Keuper series. Again, whilst 
there does not appear to be any essential difference in textural character 
between the green marls which come at the top of the Keuper and 
those lower down in that series, there is a very decided textural distinc¬ 
tion between the green marls and the overlying Rhastic shales ; the 
Tea-green marls, like the rest of the Keuper rocks, are practically un- 
fossiliferous, whereas, with the very commencement of the Avicula con¬ 
torta beds we get the first clear evidence of the incoming of a decidedly 
marine fauna, including not only forms of life that characterise the 
Rhsetic formation on the Continent, but also species of mollusca and 
reptiles which range into the overlying Lias. For these reasons, then, I 
am of opinion that in Nottinghamshire and the adjoining counties at 
any rate the line between the Rhsetics and Trias should be taken at the 
base not of the tea-green marls, but of the Avicula contorta shales. No 
doubt the Rhaetic formation as a whole, forms a stratigraphical as well 
as a palaeontological passage series between the Trias and the Lias. 
This passage is apparent at some points in this country, e.g.,&t Watchet, 
in the estuary of the Severn, There no hard and fast line can be drawn 
between the Keuper marls and the Lower Rhaetics ; green and red 
gypsiferous marls may there be seen alternating with black gypsiferous 
shales, and all are unquestionably as much Rhaetic as Keuper. Beneath 
these passage-beds are found in a general way twenty feet or so of 
green marls and calcareous marlstones (with red mottlings), which, 
under the term “ Tea-green marls, ” Mr. Etheridge, the late Mr. 
Charles Moore, and others, have proposed to class with the Rhaetics. 
For the reasons I have stated, I am inclined to agree with Dr. T. 
Wright and others, who take these “ Tea-green marls” as more 
properly belonging to the Keuper. There is, however, no necessary 
connection between the “ Tea-green marls ” of the West of England 
and the green coloured marls which occupy the same relative position 
beneath the Avicula contorta shales in the Midlands. Probably in both 
districts these green marls were once red in colour, and have since 
become bleached (and, also perhaps, calcareous in part) by the down¬ 
ward infiltration into them of some deoxidising chemical agent, 
possibly derived from the decomposition of the abundant organic 
matters of the overlying paper shales. The very general occurrence of 
twenty feet or so of greenish marls at the top of the Keuper marls in 
this country is a coincidental result of discolouration. Neither the 
stratigraphical relations, the textural characters, nor the organic re¬ 
mains of these beds, justify us in separating them from the rest of the 
Keuper and classing them as Rhsetic rocks. 
