80 



itself, which would probably be formed of carbonate of lime, has, 

 no doubt, in most cases, been removed at a later period, thus 

 causing an additional line of weakness in the slate, owing to which, 

 the subsequent exposure of the cast is very often due. 



My best thanks are due to Mr. W. Kinsey Dover, Mr. Peter 

 Harrison, and Dr. Knight, Hon. Curator of the Keswick Museum 

 of Local Natural History, for their kindness in lending me speci- 

 mens ; also to Mr. Goodchild, to whom I am indebted for the 

 drawings on the annexed plates, and for the diagrams used at the 

 Annual Meeting of the Association. 



