598 [April 1^. 



appearance of straight scratches, seem to be parts of weathered 

 cleavage lines, appearing interruptedly here and there. 



The author believes that other striae, more or less oblique and 

 irregular, and occasionally intersecting the former, have arisen 

 from cracks. The markings of this kind are rarely if ever curved, 

 differing in this respect from the glacial striae described by M. 

 Agassiz, while they are often bent at an angle, and occasionally in 

 such a manner that it is difficult to understand how a descending 

 body could have produced them. They also, many of them, have 

 flat surfaces, unlike the scorings produced by the pressure of 

 angular fragments. That such striae, or at least a large number 

 of them, were originally mere open splits or cracks, to which ex- 

 posure has given their present appearance, is suggested by the 

 author as probable, since, in many instances, they bear an almost 

 exact resemblance in width, length, angular character, and general 

 form to certain open cracks appearing on the surface of schists 

 which have been only a few years exposed, and of which examples 

 may be seen in the Penrhyn quarries on the south side, and again, 

 very strikingly, close to the Ogwyn Lake. 



Referring once more to the furrows or flutings before described, 

 the author next states that, according to his observation, these 

 markings are always parallel to the cleavage, and correspond to 

 one of the sets or series of narrow lines or joints, called by the 

 quarry -men " Water-splits," which are also parallel to the cleavage, 

 and are about half an inch apart. These water-splits are in some 

 cases quite open, in others they are seen partially filled up, and 

 in others, again, the process is farther advanced, and the furrowed 

 or fluted appearance is distinct. There is also a striking agree- 

 ment in the general width of these open lines with those of the 

 flutings, so that, on the whole, he concludes that the water-splits 

 or what he denominates " open cleavage joints," have been the 

 origin of the parallel flutings * ; and open cracks that of most of 

 the stride. He also states that the existence of scratches, properly 

 called "structural," can be distinctly proved on a small scale, 

 since even the weathered coatings of the schists, thin as they 

 sometimes are, have their own peculiar stride ; and although it 

 requires the aid of a magnifying glass to see them, they then show 

 clearly as minute delicate lines of an inch or two in length, very 

 numerous, more or less straight, and often intersecting one an- 

 other. They are, however, resemblances in miniature of certain 

 apparent scratches belonging to the rocks. 



The author then adverts to similar phenomena of striated and 

 furrowed rocks, described as occurring in America, and which 

 have been explained by Prof. Hitchcock on the glacial hypothesis, 

 but which neither that hypothesis nor the passage of ice-floes 

 over the surface are sufficient to explain satisfactorily. The view 

 advocated above, of the structural nature of such markings in the 



♦ Examples of open parallel lines occur on the right bank of the lower Llan- 

 beris Lake, and in the large adjoining quarries of Mr. Assheton Smith. 



