Correspondence — Mr. E. Brown. 585 



Mr, Mackintosh does not seem fully to appreciate tlie fact that 

 these valleys have been filled with ice, and that it has not merely 

 filled them, but passed over the fells which divide them. 



What Mr. Mackintosh will endeavour to prove from the observa- 

 tions he has recorded, I cannot venture to predict, and so will wait 

 patiently for the Mnouement. Frank Eutley, 



Geologieal Survey of England and Wales. 



ON A COLUMNAR CLAT-BED IN TIDESWELL DALE, AND ON SO- 

 CALLED PHOLAS-BOEINGS IN MILLERS DALE. 



Sir, — Allow me to express my general concurrence in the views 

 put forth by Mr. Edward Wilson, in your last number, as to the 

 nature of the altered Clay-bed in Tideswell Dale. I only awaited a 

 full report of the Eev, J. M, Mello's paper, as read to the G-eological 

 Society, before publicly expressing my belief in the volcanic nature of 

 the beds in question. I have, on two occasions during the last summer, 

 examined very carefully the Tideswell marble-quarry, and certainly 

 a more instructive section could not be desired. Mr. Wilson's descrip- 

 tion of it leaves little to be said. We have at the lower part of the 

 quarry, a coral reef converted into a bed of hard massive Limestone 

 marble ; upon that a thin layer of ash ; then a deposit of red clay, 

 varying in the open section from a thickness of about five feet at 

 one end of the quarry, to from twelve to fifteen feet at the other ; and 

 upon this, with a well-defined line of demarcation, lies the Toadstone, 

 which is probably twenty feet in thickness at the middle of the 

 quarry, but which is much wasted by denudation in other parts. 

 One inference only seems to me inevitable, viz.: that we have 

 before us in the quarry a complete record of an eruption, during 

 which lapillse were first thrown down ; then an outflow of ferru- 

 ginous mud took place ; and, finally, a bed of lava was ejected, 

 which must, in this place at least, have flowed with so steady and 

 majestic a movement that it rolled over the mud without displacing 

 it; hence the nearly horizontal line of division is clear and well 

 defined to a remarkable degree. 



One singular and striking fact seems to have escaped the notice of 

 Mr. Wilson. At the north-west end of the quarry, where the Clay- 

 bed is the thinnest, the hexagonal columns are from three to four 

 inches in diameter, and they extend ivovcx the upper to the lower 

 boundary of the bed ; whilst at the other end of the quarry, where 

 the Clay -bed has a threefold thickness, the columns are only about 

 one inch across, and they die away in the amorphous clay of the 

 lower part of the stratum. Important deductions might be made 

 from this fact as to the persistency of the heat of the superincumbent 

 Lava-bed at the time of its deposit. 



I consider that the Tideswell quarry settles for ever the question 

 sis to whether or not this bed of Toadstone, at least, was or was not 

 intrusive in its origin. No one looking at the section can fail, I 

 think, to come to the conclusion that the Toadstone-bed was a sub- 



