Shcll-Beari/ig Drift on. Mod Tryfan. — UpJunn. 83 
sequent collectors about 60 marine species have been found 
in these sections, from about 1,275 ^o 1^360 feet above the sea, 
including 27 lamellibranchs, 26 gastropods, two species of 
Dentalium, two of barnacles, one Serpula, and two species of 
the shell-burrowing sponge, Cliona.* In 1842, Darwin ob- 
served that the underlying slate, "to a depth of several feet, 
had been shattered and contorted in a very peculiar manner." 
In 1863, Lyell noted that he saw in the lower beds of the shell- 
bearing sand and gravel several large boulders of far-trans- 
ported rocks glacially polished and scratched. 
Among the great number of geologists who have treated 
more or less fully of this fossiliferous drift we may further 
especially mention Reade,f Shone, J Mackintosh§ aud Stra- 
han.[| All these authors refer the deposition of the shell- 
bearing stratified drift to marine action during a time when 
northern Wales, with Cheshire, Lancashire, and other parts 
of northwestern England, and a part of Ireland, near Dublin, 
if not much greater areas, suffered a depression of 1,000 to 
1,360 feet or more. In these districts various localities have 
been discovered where fragments of marine shells occur in 
the modified drift up to these altitudes, their maximum hight 
being on Moel Tryfan. 
Other geologists, as Belt and Goodchild in 1874, H. Car- 
vill Lewis in 1886, and Percy F. Kendall in 1892, have at- 
tributed these shell-bearing beds to deposition from the 
streams of the melting British ice-sheet, while the land here 
stood at nearly its present level, during the Champlain or 
closing epoch of the Glacial period. Y This view seems to me 
*J. Gwyn Jeffries. Quart. Jour. Geol. Soc, XXXVI (1880), 351-355. 
T. McKenny Hughes, in the same Journal, XLII (1887), 87-97, gives 
tabular enumerations of the marine fossils in the drift of Moel Tryfan 
(66 species) and of numerous other localities and districts of northern 
Wales and northwestern and northeastern England, with bibliography. 
tQ. J. G. S., XXX (1874), 27-42; XXXIX (1883), 83-132. Proc, 
Liverpool Geol. .oc, 1892-93, pp. 36-79, with eight plates (maps and 
sections) and a bibliography. 
JQ. J. G. S., XXXIV (1878), 383-397. 
§ld., XXXVII (1881), 351-369; XXXVIII (1882), 184-196. 
||Id., XLII (1886), 369-391 [abstract in Geol. Mag., third series, III, 
(1886), 331-333]. 
TJSee the present writer's sketch of "Prof. Henry Carvill Lewis and 
liis Work in Glacial Geology," Am. Geologist, II, 371-379, Dec, 1888; 
and Kendall's admirable summary of the glacial geology of England 
and Wales, in Wright's "Man and the Glacial Period," 1892, pp 137-181, 
with maps and sections. 
