200 SUPPLEMENT TO THE CRAG MOLLUSCA. 
work, of comparing all the specimens and of giving them deliberate examination. The 
Bridlington species have been examined by me either in the collection of Mr. Bean, now 
in the British Museum, or by means of specimens kindly supplied me for the purpose by 
Mr. Leckenby, to whom my best thanks are due for his obliging readiness at all times to. 
assist me with specimens. The Burgh, Horstead, and Coltishall specimens, and those from 
the Lower and Middle Glacial deposits, have all been sifted out by my son under my own 
eyes from material obtained from time to time from the various localities by Mr. Harmer, 
and most carefully guarded against intermixture or the possibility of the intrusion of any 
other material or of specimens from any other place. The March and Hunstanton speci- 
mens have all been examined by me in collections made by Mr. Harmer from those places, 
and the Nar Valley specimens in the collection of the late Mr. Rose. The Kelsea Hill 
species are principally given on the authority of Mr. J. Gwyn Jeffreys, my son’s collection 
from that place comprising only a portion of the species enumerated by that gentleman. My 
best thanks are due to Mr. Dowson and Mr. W. Crowfoot for the opportunity of examining 
the Aldeby specimens, to Mr. Cavell for the sight of specimens from the Cor. Crag near 
Orford, from Thorpe by Aldborough, and from Easton Cliff, and to Mr. Reeve for 
specimens from Bramerton. Especially to Messrs. Alfred and Robert Bell for the use 
of numerous specimens, and to the Rev. H. Canham, of Waldringfield, for his un- 
‘wearied researches in both the Red and Coralline Crags, are my thanks due. I am 
also obliged to Dr. Reed, of York, for the use of many specimens which he possesses 
from the different Crags of Suffolk, as well as to Mr. E. Charlesworth, who has throughout 
his life taken so active a part in the elucidation of the natural history of the Crags. I 
must also express my thanks fo Mr. Jeffreys for his readiness at all times to assist 
me with the loan of recent shells in his possession for the purpose of comparison. I 
have also had the assistance of my son throughout the preparation of this Supplement, 
and in the re-examination and revision to which I have subjected the determination of 
all the species given in the ‘ Crag Mollusca.’ In all the instances where not otherwise 
specified in the text the specimens are from my own collection, and of my own finding. 
In conclusion, I would add that I have studiously abstained from recognising the terms 
“Quaternary” or “Post-Tertiary.” Of the terms “ Primary,’ “Secondary,” and 
“Tertiary,” adopted by early geologists for great geological divisions, the first has become 
wholly obsolete. The term “ Secondary ” becomes yearly more and more vague, and less 
and less used to define any natural division of geological time; while the term “ Tertiary” 
alone remains convenient in consequence of the yet unbridged chasm which separates the 
beds of that division from the Cretaceous group. To introduce, however, into geology 
another division as “‘ Quaternary ” or “ Post-Tertiary ” is not merely to import a term as 
unmeaning as that of “Primary,” which has been universally dropped, but one whose 
limits cannot be defined by any constant feature, either in physical geology or in 
paleontology; and it finds a foil when some of our leading naturalists insist, as 
they have been lately doing, that we are still in the Cretaceous period. If we 
