TRANSACTIONS OF THE SECTIONS. 
587 
eye tin, or radiated oxide ; tin in spherical concretions ; have 
all been observed in a regular vein near the surface, under cir¬ 
cumstances which may authorize an inference that the alluvial 
fragments have been transported thence by a current setting 
from N.N.W. to S.S.E. 
Mr. Man tell requested the attention of geologists to the 
zoological characters of the Wealden formation, as furnishing 
the best evidence of the circumstances of its deposition, and 
the best means of identifying it in other parts of England. He 
particularly dwelt on the proofs afforded by the presence of 
fresh-water shells in the Tilgate beds, and by the absence, 
from the whole Wealden series, of zoophyta, echinida, ammo¬ 
nites, belemnites, and other decidedly marine tribes, that this 
formation was principally accumulated under the influence of 
fresh water. He illustrated the structure of the Iguanodon by 
specimens of the teeth, bones, horn, claw, &c.; and stated that 
no remains of this animal had yet been discovered except be¬ 
tween the North and South Downs ; a fact which, joined to the 
other zoological peculiarities of that district, rendered it pro¬ 
bable that the Wealden formation had not yet been recognised 
in any of the midland counties. He also exhibited a specimen 
of Hippurites from the chalk of Lewes, a genus of which he 
had formerly obtained only indeterminate fragments, and which 
he believed was now, for the first time, recorded as an English 
fossil. 
The Rev. J. Williams exhibited a very perfect specimen of 
Ichthyosaurus tenuirostris from the Lias of Somersetshire. 
The Rev. W. D. Conybeare communicated a Memoir, 
which he had drawn up in answer to a question proposed to 
him at the former meeting of the Association at York, On the 
application to Great Britain and Ireland of that part of the 
theory of M. Elie de Beaumont , which asserts that the lines of 
disturbance of the strata , assignable to the same age , are pa¬ 
rallel. 
Mr. Conybeare, in this communication, remarked on the va¬ 
rious sources of difficulty experienced in attempting to deter¬ 
mine the geological epochs to which particular elevations of the 
strata should be referred. Direct evidence is attainable in but 
few instances ; where, as in the Isle of Wight, not only the 
dislocated strata are seen in juxta-position with those which 
retain their original place, but also immediately follow them in 
the regular geological series ; and in the absence of such evi- 
