120 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 1, 



of the cleavage : such flutmgs vary in width from a fraction of an 

 inch to six inches or more, and they are usually closer together in 

 the slates of finest grain, in which the whole surface of the beds is 

 sometimes roughened by numerous ridges parallel to the strike of the 

 cleavage ; in such cases it is useless to search for fossils, for if they 

 ever existed, they must have been chopped up and destroyed in the 

 change of surface of the bed. Similar flutings and ridges are also to 

 be seen on the sides of many open joints as well as on the beds. 



There seems here to have been an irregular expansion of the rock, 

 owing to a softer and more yielding bed or an open crack affording 

 less resistance to the pressure it has been proved to have undergone. 

 INIore numerous observations are required before we can explain the 

 changes that have taken place ; but it may be inferred that these 

 changes were connected with the cleavage, because the direction of 

 the flutings and ridges on the surface always corresponds with the 

 strike of the cleavage. 



Arrangement of the cleavage-planes in the Cumbrian mountains^ 

 and their relation to the position of the beds. — Although my pre- 

 sent object only relates to the cleavage of the Cumbrian district, it is 

 necessary to give a slight sketch of the position of the strata to show 

 the connection between the arrangement of the cleavage-planes and the 

 elevatory movements which the rocks have undergone : this is derived 

 from Professor Sedgwick's various accounts of the geology of the 

 Lake district*, combined with my own observations in various parts 

 of it. 



The mountainous district occupied by the Skiddaw slate and the 

 green slate, bounded on the north by the mountain limestone, and on 

 the south by the Coniston slate and limestone, appears to consist of 

 two great areas of elevation of about equal extent, separated by a line 

 running about W.S.W. to E.N.E. from Wastwater across Borrow- 

 dale, and passing a little to the north of Scawfell and Helvellynf . 



The position of the beds throughout the northern area is tolerably 

 regular, as they dip away from an anticlinal axis on the north of 

 Skiddaw which passes through the sienite of Carrock Fell. The 

 structure of the southern area is more complicated, and appears to 

 have been determined by several elevating forces connected with the 

 eruptions of the great bands of porphyry which traverse that part of 

 the country, and of the granites of Wastdale Head, Booth, &c. As 

 the circumstances attending the position both of the beds and of the 

 cleavage in the two areas are very different, they will be described 

 separately. 



Northern area of elevation. — The two sections Nos. 1 & 2 drawn 



* Sedgwick's Introduction to the General Structure of the Cumbrian Moun- 

 tains, Trans. Geol. Soc. 2nd series, vol. iv. p. 47 ; On the FossiUferous Slates of 

 Cumberland, &c., Journ. of Geol. Soc. vol. ii. p. 1 06 ; and Letters to Wordsworth, 

 published in the 3rd edition of Wordsworth's Guide to the Lakes. 



t In dividing the Lake district into two areas of elevation, I am departing from 

 the guidance of Professor Sedgwick, who has given a section from Kendal to the 

 Eden with a single axis of elevation on the north of Skiddaw (Journ. of Geol. Soc. 

 vol. ii. p, 106). 



