384 
THE GEOLOGIST. 
wliicli jiolislicil and slriatrd the subjacent rocks, transported many of the 
erratic blocks, destroyed the pre-cxistiug alUiviuni, and left nnich boulder-earth 
in various places. 2ndly. To this succeeded a period of submcrgcuce, when 
the sea gradually advanced until ahnost the whole country was covered. This 
was tlie time of the marine drift with floating ice. The beds with arctic shells 
belonged to it, and some of tlie brick-clays are probably but the fine mud of 
the deeper parts of the same sea-bottom. 3rdly. The land emerged from the 
water, during which emergence the preceding drift-beds sufl'ered much denuda- 
tion, giving rise to the extensive superficial accumulations of water-rolled 
gravel that now overspread nmch of the surface. This movement continued 
until the laud obtained a higher ])ositiou than it now has, and became connected 
with the continent of Eurojje. Its various islands were probably also more or 
less in conjunction. The present assemblage of animals and plants gradually 
migrated hither from adjoining lands. Glaciers may have still been formed in 
favourable places, but probably never regained the former extension. 4thly. 
The land sank again until the sea in most places reached a height of from 
thirty to forty feet above the present tide-mark. Patches of forest-ground 
were submerged along the coast. The clays and beds of silt, forming the 
" carses" of the Eorth, Tay, and other rivers, were accunudated, as well as 
the post-lertiary beds of the Clyde, &c., described by Mr. James Smith, the 
shells of which agree with those of oiu- present seas. 5thly. An elevation at 
lenglh took place, by which the land attained its present level. As Mr. Smith 
has shown, this probably occurred before the Eoman invasion ; but that man 
bad previously got into the country appears from the fact that the elevated 
beds of silt near Glasgow coutaia overturned and swamped canoes with stone 
implements. 
March, 14, 18G0. — L. Horner, Esq., President, in the Chair. 
The following communications were read : — 
1. "On the Occurrence of Litujnla Crediieri in tlie Coal-measures of 
Durham." By J. W. Kirkby, Esq. Communicated by T. Davidson, Esq., 
E.G.S. 
As the Linynla Credneri of Gemitz, formerly known only in the Permian 
rocks (Lower Permian of Germany ; Marlslate of Durham and Northumber- 
land), has of late been found by "Mr. Kirkby in the Coal-measures at the 
Kyhope Winning, near Sunderland, he offers tliis notice as of interest both as 
to the discovery of another species common to the fauna; of the Carboniferous 
and Permian eras, and as illustrative of some of the physical conditions which 
obtained during the deposition of the Upper Coal-measures of the North of 
England, the occasional occurrence of this Lingula proving that marine con- 
ditions prevailed at intervals in the Durham area during the accumulation of 
those deposits. 
The species now known to be common to the Carboniferous and Permian 
fauna; (besides L. Credneri) are Terehratida Sarcnlus, Mart. {T. siiffata, Schl.), 
Spirifera Urii, Elem. {Mariinia Clamyanu, King), Spirifcrina costata, Schl. 
{Sp. odoplicata. Sow.), Camuroplioria Cnmena, Mart. {Tcrehratulci ScMothemii, 
V. Buch.), Camarophoria fjlolndh/a, Phil. {Terehratida rJwwhoidca, Phil.), — on 
the authority of Mr. Davidson ; Ci/fhere elmigfifa, Miinst., C. inortxda, M'Coy, 
Bairdia gracilk, M'Coy,— on the authority of Mr. Bupert Jones ; Gyracanthis 
formosus, Ag. — according to Messrs. King and Howse ; FinUes Brandlingi, 
Liudl., Trigonocarpon, Noeggeratlii, Broug., SigUlaria retnformis, Broug., Cala- 
miten approxiwfdus, Brong., and C. Wfequaiis (?), Brong., — collected ^by Mr. 
Howse in the lowest Permian sandstone. Erom the preceding list of Carboni- 
ferous species found also in the Permian strata of Durham, we ai-e able (says 
