278 Nofes upon the Diluvial and Alluvial Deposits of the Taffe Valley. 



sand, and is due entirely to the Severn sea. This deposition extends 

 for some distance up the Ely river, forms Leckwith moor, skirts along 

 Canton, the houses of which are on gravel, and passing through CardifiF, 

 extends beyond the Rhymmy. Its thickness it is not easy to estimate, the 

 vfater upon it is slightly brackish, and it seems on the whole to be slowly 

 increasing towards the Severn. It contains no pebbles whatever. 



Without asserting any thing with respect to the manner in which any 

 of the above appearances were caused, but simply by way of illustrating 

 our description, we may perhaps be permitted to state in what manner they 

 appear to have been formed. 



Let us suppose the mountains to have existed with nearly their present 

 form, but under water, and exposed to a current flowing permanently from 

 the north. This would form a number of pebbles, some of which would 

 remain upon the tops and concavities of the mountains, as they are found 

 round Eglwysilan church, a very few would occupy the sides, and the vast 

 bulk would be rolled along the bottom of the valley, and with more or less 

 sand, according to circumstances, be ejected upon the plain of the em- 

 bouchure, where they would be subjected either to the waves of the pri- 

 maeval ocean, or to the action of other inland currents : this would fully 

 account for all the appearances observed in the diluvial gravel. 



Next we must suppose a period at which the mountains had become 

 elevated above the surface of the water, perhaps to their present altitude, 

 while the damp and newly-raised earth was drained by a copious 

 river, whose waters would flow with considerable rapidity, and occupying 

 a large portion of the bottom of the valley, would intersect the gravel beds 

 in the manner in which we now see them to be intersected. 



After another period we must suppose the land to be drained of its 

 greatly superabundant moisture, and to be dependent for its supply only 

 upon the sources by which lands are now ordinarily moistened. Under 

 these circumstances, the river would shrink to its present dimensions, and 

 in the lapse of many centuries, cut for itself its present bed. 



Under this hypothesis, the enormous accumulation of debris will readily 

 be accounted for, as the rocks recently elevated from the sea, and sur- 

 charged with water, would of course undergo considerable and rapid degra- 

 dation. 



The valley of the Tafie also presents some appearances worth notice, as 

 illustrating the action of water upon rocks. 



There are, in various places, both upon the Taffe and Rhonddha, in- 

 stances in which the river flows over the rock in situ, generally forming a 

 fall, or at least a rapid. About such falls are a number of irregular holes 

 and sinuosities in the rock, formed partly by the water, and partly by 

 pebbles upon which it acts, which may be seen whirling round and round 

 in the holes which they thus both deepen and widen. 



Fragments of rock, similarly worn, may be observed on the summits of 



