48 Correspondence — Mr. D. Mackintosh. 



impresses a new configuration on a land-surface.^ This remark 

 applies to sea-coast action, but I think it probable that Eed Tarn 

 Cwm was mainly excavated by currents. 



(3) In Bed Tarn Cwm, and other cwms of the Lake-district, frost 

 and rain are breaking down their sides and raising the level of their 

 bottoms — in other words, these agents are doing the very opposite of 

 making a cwm. They are acting precisely the same as they would 

 on a hill-side quarry, and springs present precisely the same rela- 

 tion to cwms as they do to quarries," — in other words, springs have 

 been developed b}'-, but have not been the cause of these excavations. 



(4) Cwms, passes (the latter frequently indicating a gi'eater 

 amount of excavation at their summit-levels than towards each end), 

 and valley-expansions, form the most striking features of the scenery 

 of the Lake District, and I believe none of them can be explained 

 by the action of rain and fresh- water streams. The latter, however, 

 have excavated numerous V-shaped guUeys on the sides, or at the 

 bottoms, of the larger valleys. 



(5) Most of the lakes in Cumberland and Westmoreland with 

 which I am acquainted, especially those fed by small streams, show 

 few or no indications of sediment being transported from one end to 

 the other. The bottoms and sides of many lakes, excepting at their 

 upper ends, consist almost entirely of bare stones or rock. 



Liihodomoiis Perforations. — From the Eev. T. G. Bonney's descrip- 

 tions, I do not think he was fortunate in meeting with very perfect 

 specimens of lithodomous perforations in the Llandudno Peninsula. 

 Near the summit of the Great Orme's Head, I found groups of them 

 in a heap of newly disinterred stones, many of them more than 

 three inches in length, and very smooth and regular. In Hill Head 

 Valley, about three miles S.E. of Buxton, and between 1300 and 1400 

 feet above the sea (as noticed in my paper in the Quart. Journ. Geol. 

 Soc. for last August), I met with hundreds of perforations about 

 seven-eighths of an inch in diameter, and frequently S^ inches in 

 length. The distinction between them and structural, or weather- 

 worn holes in rocks, was very strongly marked. No land-shells 

 were to he met with in any of them, so far as I can recollect.^ The 

 Eev. T. G. Bonney has corroborated my assertion in the Q. J. G. S., 

 that most of the lithodomous perforations occur in positions protected 

 from the action of rain. D. Mackintosh. 



1 On coasts now existing, the sea makes a headland, and in time breaks it up. 



2 Or to marl-pits on the sides of drift-knolls. 



3 Mr. Cameron, of the Geological Survey, Ulverstone, lias in his possession a dis- 

 used limestone gate-post I found on a roadside near Birkrigg Moor. On one part of 

 it there is a group of deep holes more regularly ground out than a hole made by an 

 iron jumper on the same slab of rock. From one of these holes Mr. Cameron ex- 

 tracted seventeen land-shells! Did each of the snails take a txxrn at boring, while the 

 others rested from their labours ? or did one snail bore the hole, and then extend to 

 a number of brother snails the benefit of a sheltered habitation ? The late Dr. S. P. 

 "Woodward decided against the snail-theory of M. Bouchard-Chantcrcaux, and Miss 

 Hodgson, now revived by the Eev. T. G. Bouncy. (See Editorial Note to my article 

 on i'Ao/ff«.borings, Geol. Mag., Vol. IV., July, 18G7.) 



We would refer our readers to Mr. Kofe's article in the present 

 Number, p. 4. — Edit. 



