any Evidences of former Glaciers in North Wales ? 473 



The next class of appearances I have met with in North 

 Wales resembling those produced by glacier action, are the 

 striae or scratches on the surfaces of rocks. Of these I have 

 found several decided and strongly marked instances ; and as 

 they are due to various causes, and can in some cases be de- 

 monstrated not to have been connected with glaciers, it may 

 be useful to describe them somewhat in detail. 



The first I met with occurs in the Upper Silurian rocks on 

 the right bank of the Dee, in the immediate neighbourhood of 

 Llangollen. Here the true stratification is easily ascertained, 

 since it is not affected by any cleavage, though the rock has a 

 system of joints which divide the beds diagonally to the planes 

 of the surface into irregular rhombs. The beds are nearly 

 horizontal, having an average dip to the S.S.E. of about five 

 or six degrees ; and they rise to the height of from 300 to 400 

 feet, without any apparent dislocation or change in the direc- 

 tion of the dip. At the base of this precipitous hill, and in a 

 little quarry, the outcrop of the beds is seen in various places ; 

 their surfaces are generally smooth and uniformly plane, oc- 

 casionally slightly undulated. I observed the level surface of 

 one of them to be streaked or traced with strong and perfectly 

 parallel grooves or furrows, some as fine as though they were 

 made by the point of a pin, and others the eighth of an inch 

 wide, promiscuously and closely ranged alongside others of 

 intermediate dimensions. The whole surface was occupied by 

 these grooves and their intermediate ridges, and had the ap- 

 pearance of having been planed with a tool with a snipped or 

 indented edge. Some of the broader furrows were truncated 

 and terminated abruptly, and one or more narrower ones 

 seemed to be connected with and to issue from them. The 

 range or bearing of the stria? was N.N.W. and S.S.E., and 

 the breadth of surface exposed was from twenty-five to thirty 

 yards, every part of which was channeled in the manner de- 

 scribed. It was at once evident, from the general appearance 

 of the quarry, that this bed had never been exposed or dis- 

 turbed from those above or below it, since it was closely and 

 conformably overlaid by the mass above, the whole having a 

 slight inclination to the S.S.E. The furrows were also evi- 

 dently continued inwards upon the yet undisturbed portions ; 

 but to remove all doubt upon this head, 1 employed a quarry- 

 man to cut away the superincumbent bed more than a foot 

 inwards from the face, where they were found to be equally 

 clear and strong. The specimens I obtained were from this 

 part, and had never before been exposed since the original de- 

 position of the beds. The under surface of the superincum- 

 bent bed was moreover similarly though more faintly streaked ; 



