548 Miss Eyton — On Glacio-Marine Denudation. 



masses have been formed of a substance as hard as the hardest 

 sandstone. 



This bed is some hundred feet, more or less, below the level of 

 the Glacial chasms I have spoken of ; but we often find, mixed with 

 the round shingle, angular debi'is which may have been washed 

 down by former streams now vanished, or by melting snows. I 

 am inclined to believe the latter, and to see in these drifts a line of 

 partition above which we may find the remains of an ancient frigid 

 zone ; while below them we find traces of a gradually increasing 

 temperature. Specimens of Turritella communis, T. incrassata, and 

 a small Tellina, have been found in different localities along this 

 line. This bed occurs at about the same elevation and in the same 

 position as those drifts which mark the old coast-line along the 

 eastern base of the Malvern Hills, and I am satisfied with their 

 correlation. Thus the Tern basin was contemporary with, and, in 

 fact, formed a part of, the ancient Severn sea. 



Proceeding lower in the descending scale, we find that the river 

 Tern, a small sluggish stream, whose course lies exclusively through 

 sandstone and Lias, and which overflows its banks at every heavy 

 rain or thaw, so shallow is its channel, is yet bordered at a height 

 of about eighteen or twenty feet by banks of shingle, consisting 

 of such a heterogeneous mixture of materials that it is out of reason 

 to suppose them all to have been collected by the river, although 

 they may have been re-assorted and placed in their present position 

 by a former and more powerful stream. G-rey granite, which must 

 have been carried southward from Cumberland, with occasional 

 fragments of pink and micaceous granite, and flints much chipped 

 and rolled, enter into its composition. All these appear to have 

 undergone a process of scratching and grinding, more forcible than 

 anything the river could have effected, and must, I think, be the 

 remains of an old glacial drift, brought here by the waves and 

 afterwards arranged and placed by the ancient stream and its 

 tributary brooks. 



And here we find the agency of the latter at work. Passing 

 down from the hills through the high-level drifts on their way to 

 the plain, they would convey by their rapid current, much of the 

 material to the river, separating the shingle from the commingled 

 clay and silt in preparation for the sorting and bedding process, 

 to which it is next subjected. Taking into consideration the hard- 

 ness of some of the material, and the immense amount of attrition 

 which it must have taken to bring some of the pebbles to their 

 present form, there seems no alternative but to suppose it the result 

 of some such process. 



I have thus endeavoured to describe the means by which some of 

 the more extensive depressions which vary the surface of our country 

 have been formed. The same observations will generally apply to 

 those wide and deep valleys through which no river of any size has 

 its course, as the vale of Church Stretton, in Shropshire, and of 

 Todmorden in Yorkshire. Nature has her factories and her mining 

 operations as well as man, only they are upon so vast a scale and the 



