Correspondence. 139 



stone moors, near Buxton, with similarly- worn rock-surfaces, and 

 with the addition of loose shingle, and a covering of clay, not 

 derived from the limestone rock, which rock, he tell us, has suffered 

 no decomposition since the sea left the locality. Siuce I first wrote 

 on this subject Mr. Pengellyhas announced his discovery of Pholas- 

 borings in limestone cliffs, at considerable altitudes above the 

 present sea-level, and others have brought forward facts, which not 

 only show the absence, or limited extent, of subaerial disintegration, 

 but prove that the sea was, at least, the last denuding agent to which 

 the surface of the land has been subjected, ice at high altitudes 

 excepted. 



D. Mackintosh. 



DENUDATION OF VALLEYS. 

 To the Editor of the Geological Magazine. 



Sir. — Every one who lives amongst the hills, as I do, on the 

 Cotswolds, who has his eyes open, must discover parallel cases to 

 those described by Mr. Hull, in your October number ; i.e., valleys 

 commencing on high ground and descending to the sea, some having 

 rivers, others being dry. Being only a field-geologist I have no 

 theory to support, but study facts, and have my opinion, which I am 

 ever ready to alter when truth requires it. 



The valleys in the Cotswold Hills that I am acquainted with are 

 depressions in the Oolitic beds, they have a basement of clean Oolitic 

 gravel, with the edges taken off, but not formed into pebbles, proving 

 that it has never been subjected to coast or tidal action, or long con- 

 tinued attrition. Some of these valleys begin at the crest of the 

 Oolitic range, now elevated one thousand feet above the sea, and 

 gradually descend the south-east slope of the Cotswolds until they 

 reach the summit level of the Thames, four hundred feet above the 

 sea ; others are more local, descending from ground, five to six hun- 

 dred feet above the sea. 



It is clear that the dry valleys cannot owe their origin to river- 

 action ; and the river- valleys are only channels, which receive the 

 springs of the Fullers-earth or local clay beds. The action of these 

 rivers is never a denuding one, even when in flood, little solid matter 

 being carried off. It is, therefore, impossible to conceive that these 

 extensive valleys are the result of river-action, We know that the 

 Oolitic matter once formed a sea bottom, nearly, or quite level, and 

 that it is now elevated one thousand feet above the sea-level. It 

 may be assumed to have been lifted up one thousand five hundred 

 feet, and it is impossible for this to have taken place without cracks 

 in the surface, and being imequally elevated, and tilted to the south- 

 east during its elevation, sea currents must have run in these cracks, 

 and here we have an enormous power at work, quite sufficient for 

 the denudation that has taken place ; and action of this kind and 

 degree will account for the cleanness of the gravel bottoms of these 

 valleys. 



In the great estuary of the Thames, all these Cotswold valleys, wet 



