476 Mr. Bowman on the question. Whether there are 



and were also found at intervals of a few yards, wherever I re- 

 moved the overlying strata. Their direction is E.S.E. and 

 W.N.W., or 45° W. of the magnetic meridian, and at right 

 angles with the direction of the valley. But the most singu- 

 lar feature of this bed is a second system of closer, finer, and 

 more regular lines which cross the larger undulations at an 

 angle of about 70°, traversing their intermediate hollows as 

 well as their crests and sides, thus covering the whole surface, 

 and giving it a reticulated appearance very difficult to de- 

 scribe. Now and then, at irregular intervals, there is an oc- 

 casional thicker line ; or perhaps it would be more correct to 

 say that the interval between the fine lines is greater in these 

 places than usual. This double system of lines seems to ori- 

 ginate in a thin plate of somewhat different material, about 

 the eighth of an inch thick, and interstratified with the schist ; 

 for the lines cover both its upper and under surface, and the 

 still thinner laminae of which this plate is composed, are seen 

 by their darker and lighter shades, to be undulated also 

 throughout its whole thickness. This plate easily separates 

 from the contiguous thicker beds, and when removed, is 

 found to have left a sharp and perfect impression of both sets 

 of lines on each of the surfaces with which it was in contact. 

 Not only so, but the wavy lines have affected and penetrated 

 the thicker beds, rendering them more glossy, and giving to 

 the split of the cleavage a corresponding undulation which 

 gradually dies away at the depth of one-third or half an inch 

 beneath the surface. This is the more singular, as the clea- 

 vage planes cut the surface at an angle of 15° with the cor- 

 rugated lines, and throw the undulations out of their regular 

 course. There is another somewhat similar marking on the 

 surface of a second bed in the same brook, about a foot higher 

 in the series, and in the same direction or line of strike. Here 

 the lines are broader and have been deeper ; but being in the 

 direct course of the stream, they are much obliterated by the 

 water passing over them, and I did not bring away a specimen. 

 The reasoning already employed to show that the striae on 

 the Upper Silurian bed near Llangollen could not have been 

 formed by a glacier, nor by slickensides action, is in a great 

 measure applicable to those now under consideration ; it ap- 

 plies to them, if possible, with greater force, since the double 

 series of intersecting lines offers the most decisive evidence 

 that they could not have been produced by either. In specu- 

 lating as to their real origin, I will only add to the suggestion 

 before thrown out, that when this class of phaenomena shall be 

 better understood, the specimen in the bed of the Clettwr may 

 possibly throw some light on the obscure subject of cleavage. 



