KGS Paleo-Geological and Geographical Maps of the British Islands. 
. Puate XXIII. 
The Cambrian Period. 
The physical conditions of the Cambrian period over the British area contrast: 
strongly with those of the Laurentian. Previous to the deposition of the 
Cambrian beds,* those of the preceding Laurentian period had been metamorphosed, 
elevated into land-areas, and largely denuded, so that the bed of the Laurentian 
ocean (Plate XXII.) now appears as part of a large continental area, embracing the 
northern and western portions of the British Isles; while the ocean extended over 
the western districts of Europe, the whole of England, and parts of Scotland and 
Treland. 
Submerged Cambrian areas.—From considerations stated at length elsewhere,t I 
have arrived at the conclusion, that during the Cambrian period, an archzean ridge 
formed of Laurentian strata stretched through the British Isles in a 8. W. and N.E. 
direction, embracing the region of the west of Ireland, and of the Grampian Moun- 
tains, by which the Cambrian beds of the N.W. Highlands of Scotland were 
separated off from their representatives of the English and Welsh areas. This 
conclusion depends in part on the extreme dissimilarity existing between the 
representative beds on either side of the supposed ridge. I shall, therefore, describe 
the beds under the two types which I have called, on the occasion referred to, 
those of the “Caledonian,” and “ Hiberno-Cambrian.” 
Cambrian Beds of the Caledonian type.—These are restricted to the north- 
western Highlands of Scotland, where they occur interposed between the Laurentian 
rocks below, and the quartzites, limestones, and shales of the Lower Silurian beds 
above. They consist of great beds of red and purple sandstone and conglomer- 
ate, generally in nearly horizontal positions, forming bold escarpments, and isolated 
pyramidal masses. The pebbles of which they are mainly formed consist of various 
kinds of gneiss, schist, porphyry, and quartzite ;—presumably derived from the 
adjoining land-areas of Laurentian strata. Professor Ramsay considers these beds 
to have been deposited in the waters of an inland lake, of which the outer Hebrides 
formed the western margin.t In this view I concur. No fossils have been found. 
in these Jacustrine beds. 
Cambran Beds of the Hibernu-Cambrian type.—These are vastly more extensive 
than the former ; and, though they only crop out to the surface in a few places, may 
be presumed to underlie nearly the whole of England and Wales, as well as the adjoin- 
ing parts of Kurope. They consist of green and purple massive grits, quartz rocks 
and slates, with, occasionally, pebbly beds ; and as the fauna is distinctly marine the 
* T use the term Cambrian to include the Longmynd, Harlech, and Llanberis beds, together with the: 
overlying Upper Cambrian Lingula flags, as the fauna of the latter has been shown by Dr. Hicks to. 
be present in the former. I therefore take the base of the Silurian series at the Tremadoc slates. 
+t “Quart. Journ., Geol. Soc.,” May, 1882, p. 210, and Brit. Assoc. Rep. (1881, p. 642.) 
} “ Phys. Geology and Geography of Great Britain,” 5 edit., 283, é&e. 
