BRITISH ASSOCIATION MEETING. 
483 
same fact. I liardly ever saw it in situ Avithout finding two contiguous 
iustauccs — /. e., two pairs of polished surfaces sometimes witliin half an iuch, 
sometimes two feet of each other, the intervening sjjace being occupied by 
rock more or less idtcred in character, and generally more compact. The phmes 
never agreeing with the stratification, and often nearly perpendicular to it. I 
never saw any termination of the polished planes, so that I should suppose 
they intersect whole mountains. In granite and trap the surfaces I have seen 
were far from plane, and exliibited a diiTcrent substance rather like steatite or 
soapstone (so m serpentine). In sandstone the polish is such as coidd not be 
produced by ;u^ificiid means (without vitrifying) ; but, however sleek the sur- 
lacc, it always exhibits strise, sometimes parallel, but often inclined at various 
angles. The following questions seem worth following up, to obtain more 
light on the subject : — 
1. Are all rocks found to exhibit these siu-faces ? 
2. K so, are the circumstances alike in the main ? 
3. If not, what sort of rocks seem excepted ? 
4. Are conglomerates exempt ? Is chalk ? Is rock-salt ? 
5. Is it a question of age ? Is it as common in Old Red as in New ? 
6. If in roofing slate, what is its relation to cleavage ? 
7. If in trap-dikes, does it crop the dike ? 
8. If in soft sQurian shale ("niudstone") does it harden t^at ? N.B. It 
does not seem to .dter coal at all, and I have seen something very like it in 
clay, not so hard as French chalk. 
9. Is it found to pass into contiguous rocks, that overlie — e. g., from Moun- 
tain-limestone into Old Red sandstone. 
10. Does it ever pass into rocks lying conformably ? 
11. Does it affect the accidental minerals of the rock through which it 
passes — e. g., Bari.i:es in Mountain-limestone ? 
12. Does crystaUizatiou interrupt it, or vice versa? 
13. Are the stris universal ? 
14. Does it never correspond with stratification ? 
15. Are the surfaces coated with a different substance, or is it merely the 
rock itseU' altered ? 
16. Has it been seen on the opposite sides of valleys, or of mountains ? 
17. Have the apparently parallel paii-s been found to meet, and so come to 
an end ? I have seen something Uke this. 
!Mr. Cunningham asserts that here they form a barrier to springs of water. 
Is this general ? 
AUow me to commend to the notice of tourist -geologists Llysfaen, near 
Abergele, as exhibiting witliin a very small compass five very remai-kable and 
perfectly distinct di-ifts ; also a good mountain-limestone fossil station, with a 
good flora (silui-ian fossils near) between Rhyl and Llandudno. 
Additional Queries. — 18. Does the " slick" or polished sui-face indicate a 
fault? 
19. Is the " slick" ever intersected by mineral veins ? 
20. Are the perfectly level "speculai-" surfaces and those which, though 
glossy, are uneven, to be referred to the same agency ? 
21. Do they ever coincide with the stratification, partings, cleavage, "lamina- 
tion," or " foliation" (E. Forbes), and are they to be considered as absolutely 
sui generis, or to be classed, with some of these ? 
