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ME. PEESTWICH ON THE GEOLOGY OF THE DEPOSITS 
Clansilia plicatula, and Vitrina diaphana , shells now living in France but not in 
England, and all of which Mr. Gwyn Jeffreys has recognized in my collection from 
Menchecourt*. The last-named shell is more especially alpine ; whereas the Cyclostoma 
elegans, which abounds at this place, and has not been found at either St. Acheul or 
Biddenham, has a range essentially southern, not being now found north of central 
Germany f. 
Besides the land and freshwater shells, the following species of marine and estuarine 
shells have been met with at Menchecourt : — 
Buccinwm undatum. Littorina squalida. Cardium edule. 
Fusus. Nassa reticulata. Ostrea edulis. 
Littorina littorea. Purpura lapillus. Tellina Balthica. 
These, like the freshwater shells, present, with two exceptions, no differences from the 
recent species. These exceptions are, according to Mr. Gwyn Jeffreys, L. squalida , 
which is now absent from our shores, but lives on the coast of Norway ; and the 
T. Balthica , which is of the northern variety. Both these shells are found in other 
postpliocene deposits of this country, and range back as far as the Crag. 
But the most important shell at Menchecourt is the Cyrena ftwminalis , of which 1 
have found three specimens^. This mollusk, as is well known, now lives in the Nile and 
in mountainous streams of central Asia — a range presenting great extremes of climate. 
It is evident that at Menchecourt the waters were saline or brackish. As in the 
estuary of the Thames at present, the Cardium edule and the Littorina littorea were then 
common shells. The Buccinum undatum was far from rare. Of the Ostrea I have only 
found one dwarfed specimen. Associated with these are numbers of Limncea , Helix , 
and other freshwater and land shells, washed down into the estuary by freshets of the 
old streams or rivers. On some of the large flints in bed e (former paper, p. 284), which 
are as fresh and perfect as though just taken from the chalk, I have found attached the 
opercula of Bythinia. These flints were probably carried down undisturbed with the 
Bythinia itself attached, from the bed of some small tributary stream, by the agency of ice. 
That shells should be found at Menchecourt and Mautort and not at Montiers and 
St. Roch, arises, I imagine, from the overwhelming floods, and from the large mass of 
constantly shifting shingle along the bed of the old river, which would be influenced 
thereby throughout the length of its main channel above tidal influence. But where 
the tide met the current, near Abbeville, the force of the latter being much checked — 
especially where any projecting land sheltered portions of the river from its full effect, 
* A curious feature of the period is the abundance of two species of slugs. In some of these beds, and more 
especially in the Loess, at Menchecourt I had found numbers of small oval calcareous bodies, for the origin of 
which I was at a loss to account until Mr. Gwyn Jeffreys recognized them as the calcareous grains found in 
the Arion ater. The small shelly shield of the Limax agrestis is also found, but less abundantly. — April 1864. 
f Gwyn Jeffreys, ‘ British Conchology,’ vol. i. p. 805. 
X It is singular that in the greater number of places where the Cyrena fluminalis occurs in a fossil state 
the waters have been brackish or estuarine, as at Grays, Chislet, Abbeville, and in Norfolk (the Crag) &c. 
