158 David Milne, Esq., on Polished and Striated Bocks, 



It is material to observe, that whilst all along the east side of the 

 road, there was a general surface of smoothed and polished rock for 

 about 80 yards, spots were here and there found, wanting that ap- 

 pearance. Those parts of the rock had their rough faces uniformly 

 towards the south, or more generally south-west. They were ap- 

 parently on lines of natural fissures in the rock, which fissures 

 (termed hacks by quarrymen) run here WNW. by compass. To- 

 wards the eastward, the porphyry is much intersected by these fissures, 

 and is in its own substance very friable ; whilst, at the narrowest 

 part of the trough, the porphyry is exceedingly compact. In many 

 of these fissures I observed that portions of the rock had been re- 

 moved, the removed portions having invariably been taken from the 

 south sides of the fissures, thus : 



Fig. 2. 



The letters a represent the fissures, from the south sides of which 

 portions of rock had been removed ; the letters h represent the ge- 

 neral line of smoothing along the east side of the gully. The sides 

 of these fissures facing the south had evidently not been rubbed, but 

 preserved their original roughness in most cases. Indeed, I found 

 only one exception, and that was, where there was an unusually 

 larger portion of the rock removed from the south side of the fissures 

 in the way represented at h c. 



In regard to the degree of smoothing and polishing, it was much 

 greater at some places than at others. Towards the west, where the 

 gully was narrowest, and the rocks were hardest, the rocks are the 

 most highly polished. Towards the eastward, where the rock is 

 friable, the rocks, though greatly rubbed, rutted, and worn down, 

 are not nearly so smooth. 



The axis of the gully between these smoothed rocks, is not exactly 

 a straight line. Though the direction along the east side of the 

 gully is, generally speaking, NW. and SE. by compass, the line, 

 on the whole, seems to form a gentle curve, running at the north 

 end WNW., and at the south end SSE. Even in this curve there 

 are occasional bulgings out beyond the general line, arising, ap- 

 parently, from the harder nature of the rock, which, on that account, 

 seems to have yielded less to the rubbing agent, whatever it was ; 



