Lyell Collection
Quarterly Journal of Engineering Geology and Hydrogeology
Lyell Centre  |   Lyell Collection  |   Subscriptions   |   Geological Society  |   Email alerts  |   Online bookshop  |   Help

Keywords:
Author:
Advanced search>>
This Article
Right arrow Full Text (PDF)
Right arrow References
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Search for Related Content
Quarterly Journal of Engineering Geology and Hydrogeology; 1984; v. 17; issue.1; p. ii-iv;
DOI: 10.1144/GSL.QJEG.1984.017.01.01
© 1984 Geological Society of London

Photographic Feature

Rock jointing at the Penmaenbach Headland, North Wales

The mountainous headland of Penmaenbach has long been an obstacle to communications west of the River Conway in North Wales. Before 1826 the headland was passed either by crossing the beach at low tide (Fig. 1), near where the photograph was taken, or by way of the more difficult inland route over the Sychnant Pass between Conway and Penmaenmawr. Also shown in Fig. 1 are the 1826 Telford Road, the tunnel through the headland for the Chester and Holyhead Railway, built in 1846, and the short tunnel for the existing A55 road constructed in 1932.

As an important part of its plan to improve the road system in this area HM Welsh office are implementing a substantial improvement scheme for the A55 coast road that will require a second road tunnel through the headland.

The rock seen in the photograph is a rhyolite, thought to be the vent of a volcano penecontemporaneous with the Ordovician rock in the area. Being significantly more resistant to erosion than the surrounding sediments the vent is now exposed as the headland with near vertical cliffs to the beach.

The rhyolite is exposed in many place allowing examination of the jointing pattern. Measurement of discontinuities reveal no generally preferred orientation, although in localized areas discreet joint sets are readily identifiable. In the area of the photograph three sets can be clearly recognized plus some random jointing. The sets are designated S1 S2 and S3 are highlighted in Fig. 2 by omitting all but one set

...

This 250-word extract was created in the absence of an abstract.