Chap. II.] 
METAMORPHIC CAMBRIAN ROCKS. 
35 
MetamorpJiic Cambrian Rocks. — It has been stated that there are no 
rocks in South Britain of more remote age than the basement sediments 
which occupy the Longmynd and the parts of North and South Wales 
already spoken of. Por a long time, indeed, it was believed that the 
schists and quartzose and felspathic rocks of the Isle of Anglesea, judging 
from their crystalline character only, were more ancient than any of the 
masses of the adjacent mainland*. Such, however, is not the case, The 
preexisting Laurentian rocks, out of whose materials were formed the 
strata of the Longmynd in Shropshire, of the Llanberis, Bangor, and 
Harlech mountains in North "Wales, and of St. David's in South Wales, 
having long ago subsided beneath an ancient ocean, and having been 
covered over by the Cambrian strata of which we now treat, are in the 
British Isles apparent as dry land only in the North- Western Highlands 
and Hebrides (see above, p. 9). 
Contorted Crystalline Schists at the South Stack Lighthouse, Anglesea. 
By the observations of the Government Geological Surveyors, and chiefly 
by those of Professor Ramsay and Mr. Selwyn, it has been ascertained that 
the hard and crystalline rocks of North Wales, whether on the coast of 
Carnarvon Bay, ranging southwards to the island of Bardsey, or in the isle 
of Anglesea, are simply altered portions of the same slates and grits which 
constitute the base of the Cambrian deposits in the counties of Carnarvon 
and Merioneth. In other words, these old strata have, by the intrusions of 
* See the G-eological Maps of England and as well as the ' Outline of the Geology of England 
Wales, by William Smith and Greenough, and and Wales,' by Conybeare and Phillips, 
even the edition of the latter published in 1839; 
D 2 
