366 
PROCEEDINGS, 1871 — 1877. 
This process is continued two or three years, at the end of which 
time a deposit of rich soil, sometimes three or four feet in thickness, 
has been accumulated. The physical features of the district have 
been greatly changed by embanking the rivers, which is said to have 
been done in the reign of Edward III., and again by Vermuyden's 
drainage of Hatfield Chase in the 17 th century. Prior to that time 
the country must have been overflowed by eveiy tide, and the whole 
district been an expanded series of bogs and marshes. In an appendix 
the author gives an analysis of the ancient and modern warps, and 
eighteen sections of the alluvial deposits obtained in boreings and 
well sinkings extended over the district. 
Mr. J, Pv. Dakyns described the sections exposed at Falcon 
Glints, and in the neighbourhood of the Old Pencil Mill below 
Cronkley, in Upper Teesdale. In each of these the uppermost beds 
consist of whiusill beneath which are altered limestones and shales. 
At the base of the latter an altered breccia more or less similar to 
breccias which had been found in other parts of the country separating 
the Carboniferous series from the Silurian rocks, and he was led 
to the inference, which was afterwards demonstrated to be correct, 
that the Silurian rocks formed the bed of the valley. 
Mr. W. Percy Sladen, now honorary secretary of the Linnean 
Society of London, contributed a paper on the Genus Poteriocrinus 
and Allied Forms. Twenty-four species described by Miiller, Phillips, 
Austin, McCoy, and De Koninck, were enumerated. These were shown 
to possess characters which necessitate their re-distribution into the 
Genus Poteriocrinus, Dactylocrinus, Scaphiocrinus, and Zeacrinus, 
the second a new genus suggested by the author, who remarks that 
it is necessary to bear in mind that naturalists have been content 
hitherto, in the classification and grouping of crinoids, to base their 
determinations upon differences in the arrangements and relative 
proportions of those plates alone which enter into the composition of 
the calyx or body-wall of the crinoid, and have neglected almost 
entirely any consideration of the general morphology, or physiology 
even, of the forms to which they have assigned type characters. The 
continuous increase which has been made of late years in palajon- 
tological knowledge has rendered the solution of many problems 
