EXCURSIONS. 
411 
of Eskdale (Cumberland) and Andesitic rocks from the Borrow- 
dale Series of the Lake District. 
Close to the Craig Nant Quarries the ancient earthwork of 
OfTa's Dyke was crossed, and could be seen extending across the 
country in both directions for some distance. 
From Craig Nant the party drove towards Llansantffraid 
Ghm-Ceirios:, ahghting about half a mile above the village 
to examine a quarry in the Hirnant Limestone of the L^pper 
Ordovician, where a few specimens of Orthis were found in the 
more calcareous portions. 
The road from Craig Nant to Glyn runs in its upper part 
through a vaUey which cuts through the watershed, and is now 
almost streamless and may possibly be a glacial overflow channel. 
It is at a height of 1,157 feet above the sea. 
After a light lunch at Glyn the quarries at Cae Deicws were 
visited. 
These are excavated in a pale buff- coloured felsite containing 
porphyritic crj^stals of quartz and felspar. 
The columns into which this rock has broken, as the result 
of contraction due to cooling, have assumed an exceedingly 
unusual form, being strongly curved. The rock is known locally 
as " China-stone." 
The Cae Deicws Quarries are near the summit of a steep 
slope overlooking the Glyn Valley, and at the foot of the hill is 
another excavation in a somewhat similar rock. Here the 
junction of the igneous wath the surrounding sedimentary rocks 
(Bala Slates) can be seen. Xear the line of junction many 
fragments of limestone from the Bala Beds are included in the 
igneous rock. These fragments are little altered and are associ- 
ated with numerous angular pieces of the felsite. It would 
appear that the marginal matter is of an ash}^ nature, and it 
was suggested on the ground that the felsite which occupies 
the centre of the quarry was a dyke intrusive in the ash beds. 
Mr. Lomas, however, describes the section thus : — " The 
line of junction has evidently formed a plane of movement, 
for the marginal portions are sheared and contain fragments 
of slate, China-stone, and limestone."* 
* Proc. Geologists' Assn., Vol. XX., Ft. 7, p. 494. 
