474« Geological Society. 



glomerates. The former are more or less compact, sometimes passing 

 into phonolite and basalt, and occasionally assume a columnar struc- 

 ture. The conglomerates are composed of angular fragments of tra- 

 chyte, imbedded in a tufaceous paste. The inclosed portions are some- 

 times softer than the cement, when the rock assumes a honeycomb 

 appearance, but they are more often harder, and stand out in bold 

 relief. The conglomerates rest upon and alternate with the trachyte, 

 and in some places are intersected by basaltic dykes. Veins of car- 

 nelian and chalcedony are stated to be contained in the igneous rocks, 

 and near Filbornou to pass through the conglomerate, traversing both 

 the basis and the included fragments. These conglomerates are 

 considered by Mr. Strickland to have been accumulated by water, and 

 the contained fragments, though commonly angular, are sometimes 

 rounded, and included in finely laminated volcanic sand. On the 

 Asiatic side of the Bosphorus the igneous rocks commence en masse 

 at Kavak, under the old Genoese Castle, and extend to Yoom-bornou 

 on the Black Sea, or perhaps further 3 and on the European side they 

 commence on the north of Buyukder6, and also extend to the Black 

 Sea. Besides these great masses of igneous products, trachytic and 

 trap dykes were observed by the authors traversing the Silurian rocks 

 at Baltalimani, in the hills above Bebek, at Kiretch-bornou, and the 

 base of the Giant's Mountain. 



3. The Tertiary deposit commences -immediately on the west of 

 Constantinople, and extends inland about three miles, till it meets the 

 transition formations, and ranges along the north coast of the Sea of 

 Marmora for many miles, its western limit being at present undefined. 

 Id is best exhibited in the quarries at Baloukli and Makri-kuei, where 

 it consists of horizontal beds of soft, white, shelly limestones and marls, 

 resting on sand in which no fossils have been observed. Near Con- 

 stantinople the deposit was apparently accumulated in an aestuary, 

 for it contains a species of Cardium, and considerable numbers of a 

 fossil considered to be a Cytherea, the whole being associated with 

 land and freshwater shells, some of which resemble recent species. 



Along the banks of the Bosphorus the authors observed no traces 

 of a tertiary formation ; and consequently infer that this channel was 

 opened at a comparatively very recent period. 



The only ancient alluvium mentioned in the memoir is an extensive 

 and thick deposit of ferruginous clay, sand, gravel and boulders, rest- 

 ing upon the Silurian or transition rocks. It commences a few miles 

 north of Constantinople, forms the subsoil of the Forest of Belgrade, 

 and apparently skirts the southern side of the Lesser Balcan range. 



Dec. 14.— A paper "On Impressions in Sandstone resembling those 

 of horses' hoofs," by Charles Babbage, Esq., and communicated by 

 the President, was first read. 



During a recent visit to Dowlais, Mr. Guest mentioned to the 

 author, that in the channel of a stream on the extensive moor 

 called Fwll y Duon, and about seven miles from Merthyr Tydvil, 

 there were many impressions considered by the country people to 

 have been made by horses' hoofs. The stratum of sandstone in which 

 they occur is called the Farewell Rock, being the lowest bed of the 



