Vice-President’s Address. 281 
conspicuous a feature in the geology of the Jurassic- Wealden 
period, 59,400,000 years. 
The New Red Rocks (Dyas and Trias).— At several localities 
in Britain, as is well known, a considerable thickness of rock, 
formed mainly under desert conditions, underlies the Jurassic 
Rocks proper. Their upper limit is marked by the (Marine) 
Rheetic Rocks, which contain a very well-defined fauna, and 
which graduate upward into the base of the Jurassic Rocks. 
Their lower limits are extremely variable—perhaps on account 
of their having been formed under terrestrial conditions— 
perhaps partly on account of more-than-usually-local flexures 
of the subjacent surface arising through differential subsi- 
dence. The ageregate maximum thickness may be fully 
4000 feet; yet the higher members overlap in succession 
every one of the lower in one part or the other of Britain. 
Wherever the series exists, it is practically one conformable 
series from the top to the bottom. On the other hand, the 
base les in one part or another with a violent unconformity 
upon every rock older than itself. 
Low down in the series occurs, in places, a band of 
Magnesian Limestone, whose fossils, and especially the 
Invertebrata, show a certain affinity with those of the 
Carboniferous. This affinity, however, is by no means as 
close as was believed up to a few years ago, as many fossils 
supposed to have come from the Dyas really came from 
stained rocks of Carboniferous age. The fossils of the 
Magnesian Limestone, whatever their affinities may be, are 
sufficiently marked in character to enable one to trace the 
English Magnesian Limestone, by the aid of its fossil 
contents, far to the east of the British Isles. On the Con- 
tinent, therefore, we can trace the upper limit of the New Red 
by means of the Rheetic strata into central Europe, and we 
can follow the Magnesian Limestone by the same clue 
almost as far. Important changes in the nature of the 
beds between these two platforms set in; and in place of 
a series of desert-formed rocks we find, in the Tyrol, thick 
masses of Marine Limestone. I have before suggested that 
we should employ as far as possible a uniform system in 
comparing strata of different ages, and should take every- 
