f GEOLOGY. 301 



beaches, they would probably have been rounded by the action of the 

 waves ; and if great marine floods ever existed, driving before them such, 

 great masses of debris, the same rounding action would have resulted. 

 Such large blocks of rock are not moved along ordinary sea-bottoms by 

 tidal or other actions ; and, considering their size, angularity, polish, oc- 

 casional scratchings, and the matrix that encloses them, the author believes 

 that they were deposited from icebergs, derived from glaciers that origi- 

 nated in the ancient land of the Longmynds, and overlying Lower Silu- 

 rian strata, west of the Stiper stones. These rocks were once covered un- 

 conformably by more than 3000 feet of Upper Silurian rock, and probably 

 by a large part of the old Red Sandstone besides. These had, therefore, 

 been removed by denudation before the deposition of the Permian strata. 

 A great fault of more than 3000 feet runs from north-east to south-west, 

 immediately east of the Longmynds. It is a downthrow on the west of 

 later date than the New Red Sandstone, and the range of the Longmynds 

 was, therefore, from 3000 to -iOOO feet higher at the Permian period than 

 now with reference to the existing levels of these formations. Traces of 

 the same glacial action occur in the Bunter Sandstone, in a portion of the 

 pebble-beds that lie between the lower and upper variegated sandstone, 

 and also at the base of the white sandstones that underlie the new red 

 marl in the neighborhood of the Abberley Hills. 



In addition to the above, Prof. Ramsay presented another paper, the 

 object of which was to prove that the ice of the greater glaciers of North 

 Wales was about 1300 feet thick; that the valleys of Llanberis, Nant 

 Francon, &c., were, in fact, filled with ice, at least of that thickness. This 

 was inferred by the height on the walls of the valleys at which polished 

 surfaces, and parallel grooves and scratches, were plentifully found follow- 

 ing the main direction of the valleys, without reference to the minor lateral 

 valleys. During the subsequent depression of the country to a depth of 

 2300 feet the cold still continued, and glaciers on a smaller scale passed out 

 to sea and deposited what may be callt d marine moraines. Farther out 

 at sea, on Mod Try fan, marine deposits with shells were formed, either 

 contemporaneously with these marine moraines, or during subsequent os- 

 cillations of level by the rearrangement of the moraine matter. 



After the re- emergence of the land, the drift was cleared out of the 

 greater valleys by a second set of glaciers. These gradually decreased in 

 size, evidence of which may be found in the moraines that occur in the 

 valleys at different levels. In Cwm Glas, in the pass of Llanberis, there 

 are several of these moraines left by a retiring glacier, which finally dis- 

 appeared in the highest recesses of the valley immediately north of the 

 ridge of Cribgoch. 



ON THE DEPTH OF THE PRIMEVAL SEAS. 



Prof. Forbes, in a communication to the Royal Society, states that, 

 when engaged in the investigation of the bathymetrical distribution of 



