and " Roches Moutonn&s" 489 



ture ; a mass of slate between two such bands must have its 



bedding parallel to them In many cases we can ascertain 



the lines of the true beds by an internal and secure test. The 

 planes of the slates are often marked by parallel stripes of 

 different colours. Among the finer green slates these stripes 

 are generally paler than the other parts of the rock ; and as 

 they mark the original lines of sediment, they are therefore 

 parallel to the true bedding; indeed they generally mark the 

 passage from one bed to another. Sometimes these stripes 

 are seen on slaty laminae, cutting through pyritous bands with 

 shells and corals ; and in such cases the stripes upon the 

 smooth surfaces of the slates are alwavs parallel to the fossil 

 bands*." 



Now, though in the case we are considering the bedding is 

 very obscure, we have for our guidance (i the internal and 

 secure test " above mentioned, the true direction of the beds 

 being marked by parallel stripes of different colours. These 

 facts are stated thus fully, because there are still some who 

 maintain that rock-striation is structural, or in the direction 

 of the beds, and has been produced by the unequal wearing 

 of the constituent laminae under the action of water, and is 

 not due to the passage of ice or boulders across the surface. 

 But it is unnecessary to enter into a discussion of views so 

 entirely opposed to established facts f. 



III. At Birthwaite Station. 



The next example is seen at Birthwaite, the present ter- 

 minus of the same railway, within the grounds belonging to 

 the station. Here the surface of the Lower Ludlow Rock has 

 been stripped of its covering of detritus to an extent of 45 feet 

 in a direction perpendicular to the striae, and of 15 feet in a 

 line with them. This surface is similarly divided into several 

 rounded, smooth, and polished bosses or eminences of an ellip- 

 tic form, whose greater axis is in the direction of the striae, or 

 across the surface; and which, though less regular in form, 

 have the same "moutonnee" character as at Jacob Wood. 

 The prevailing direction of the striae and grooves is magnetic 

 N. and S., or about 24° W. of true N. Many, however, are 

 inclined to this direction at various angles. On the western 

 side the direction is chiefly N.W. and S.E., but in the middle 

 and on the eastern side they have the range above stated, 



* Third letter addressed to Mr. Wordsworth in Hudson's Guide to the 

 Lakes, one of the most interesting and valuable books of this class which 

 we have ever met with. 



f See Prof. Oldham's Address to Geol. Soc. Dublin, 1850, p. 27, and 

 the Journal of the Geol. Soc, vol. ii. 



