TIDESWELL DALE QUARRIES. 5 



Grotto near Bad-Bertrich, in the Eifel district. It is a passage 

 cut through a lava stream which flowed from one of the neigh- 

 bouring tertiary volcanos. Lava columns form the sides of the 



Fig- 3- 



passage, the roof exhibiting transverse sections. They are divided 

 by transverse joints at regular intervals, and the angles and edges 

 of the sections having fallen away, the columns resemble piles of 

 Gruyere cheeses. This falling away of the edges and angles results 

 partly from the action of the weather, and partly from a pre-dis- 

 position in the segments to break away at these points. For my 

 own part I cannot see how weathering can wholly account for the 

 spheroidal structure. I append an interesting letter on the subject 

 from Mr. Ward. 



Close by the Cheese Grotto, the bed of the Uesbach is com- 

 pletely tesselated with the transverse sections of columns, which 

 are remarkably regular. 



The limestone strata underlying the toadstone contribute 

 several important items of evidence as to the geographical and 

 climatic conditions of the period. These strata, as has been said, 

 are coralline, and there can be little doubt that they formed a 

 coral reef in the limestone sea of the Carboniferous period. 



