440 
tunity is presented. If in such situations the gravel or soil 
is removed from the upper surface of the rock, and the rock 
itself washed with water, the groovings become apparent. 
Those in the specimens I procured at Langley were quite 
prominent, even without wetting the rock, especially when 
viewed by a side light. They were precisely the counterpart 
of the engraved groovings described by Professor Agassiz, 
in Switzerland, and by Professor Locke, in America — so 
similar, indeed, that they have passed for the originals whence 
these eng-ravinofs were made. Of these two eno^raved ex- 
amples, the one, it must be borne in mind, was brought by 
Agassiz from under a glacier — the other was considered 
by Professor Locke to afford evidence of the motions of a 
body, the conditions of which he concludes must be the same 
as that of a glacier. 
Besides the larger groovings, which vary in size from a 
quarter of an inch to one or two inches, there are numerous 
scratches such as would be produced by sharp angular points. 
Both these and the groovings are often continuous for a dis- 
tance of several yards, and are sometimes suddenly broken off 
— as if the abrading angle had been snapped ; and in one 
instance near Pont Aber Glasslyn, of which I made a 
drawing, the moving force which grooved and scratched 
the rock appears as if it had been forced aside by a pro- 
jecting knob of rock. 
Boulders with flat sides are found in Great Britain as well 
as in Switzerland, and the scratches on their surface seem to 
indicate, that they had been moved so as to come in contact 
with angular points in different directions. 
The most probable places to look for these grooved, 
polished, and scratched conditions of rock, are on the sides 
of valleys, and especially where the rocks are of a hard 
nature ; and in every instance which I have yet seen, the 
groovings have been parallel to the direction of the valley. 
