ROCKS OF CAERNARVON. 683 
Fig. 1.—Section of Twt Mill, Caernarvon. 
§.E. N.W. 
wi 
a, Cambrian Conglomerate. ce’. Lower Caernarvon beds. 
* Beds of quartzite and divisional planes suggestive of bedding. 
quarry in the first field on the N.K. of the hill, which we shall 
refer to as the Twt-Hill Field quarry, it is seen flanked on the 8.E. by 
sandstone, grit, and conglomerate (see figs. 1&2). Itis thrown back 
Fig. 2.—Section N.E. of Twt Hill, Caernarvon. 
§.E. N.W. 
Twt Hill 
Field Quarry. seen to 8.W. 
7 
HN ip 
i 
\ 
seamed srt 
a’. Sandstones. ; c'. Lower Caernarvon beds. 
a’, Conglomerates. } ORmOnIAD, * Felsite, with platy structure. 
by a small fault crossing the ridge N.E. of Twt Hill, with a down- 
throw on the E., so that it is found in the quarry by the highest new 
road above Yscuborwen with the same grit and conglomerate on its 
Fig. 3.—Section in Quarry above Yscuborwen, Caernarvon. 
8.E. 
N.W. 
Quarry. New Road. 
< 
AN 
ah 
ie i 
Ta ad =| 
ee AE 
pee nin BEE ONGS 
al! a’ s c d 
5B 
os 
4 
” 7 I? 
. Sandstone and grit. : ce’. Lower ; 
a” Sandsto grit. | oO. brian. wer Caernaryon beds 
a', Conglomerate. d. Greenstone. 
S.E. flank (see fig. 3). This fault coincides with a greenstone dyke 
running 8. 20° E. and seen in the quarry; and there is also seen in 
the same quarry another fault running up to the 8S. end of the dyke 
(fig. 4), nearly at right angles to it, and dropping the grit a little on 
the § 
The coarser variety of the Twt-Hill rock has been largely quarried 
behind Llysmeirion and Richmond Hill, and is again seen about half 
