of Edinburgh, Session 1878-79. 265 
scratched, in a direction nearly E. and W., or E.S.E. and 
W.S.W.” 
Much to the same effect, Mr John Henderson of this city, an 
excellent practical geologist, refers to two localities in the Pentlands 
where clay beds occur full of gravel and hard pebbles. One of 
these places is GlencOrse, at a height of 900 feet, where he says 
there “is a stiff reddish clay full of well-rubbed and scratched 
stones, and differing in no way from the boulder-clay of the lower 
districts.” The other locality is 3 miles distant, at a height of 
about 1100 feet, where (Mr Henderson says) the clay is of the same 
character as the last-mentioned, and covered by a great deposit of 
gravel and boulders. 
That ruts and striae on the smooth surface of a rock can be pro- 
duced by the passage and pressure of hard angular stones, is a fact 
established by many cases carefully observed. I remember many 
years ago having witnessed the effects produced by the giving way 
of a large embankment on the North British Bail way at Dunglass 
Burn. The culvert under the embankment had become choked. 
Water accumulated on the upper side, till at length the embank- 
ment gave way. The materials composing it rushed down the valley 
with much force ; Bocks and large blocks of stone along the valley 
were scratched and rutted by the debris passing over them. I 
thought the circumstance so instructive that I procured one of the 
large striated blocks, on which no less than 50 or 60 striae had been 
made, and deposited it in the Museum of this Society. I have sought 
for this specimen, to show it this evening, but without finding it. 
III. Information obtained by Study of Boulders. 
Whilst considering the agency which produced strice on rucks, 
it is not irrelevant to keep in view the light thrown on the subject 
by Boulders. 
Boulders are, like striated rocks, found at all levels, from the sea- 
shore to the tops of the highest hills. Many of these boulders are 
traceable to parent rocks situated in the western districts, and there- 
fore show, as the striated rocks do, an agency of great power which 
moved from the west. For example, the mica slate boulder on 
the Pentland Hills, 8 or 10 tons in weight, at a height of 1400 
feet above the sea, first noticed by Mr M‘Laren, must, as he says, 
2 H 
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