the Geological Structure of North Wales. 257 



have been flowing in their existing channels, and producing the effects 

 of diurnal erosion (marked by deltas gradually filling up lakes, and 

 by other alluvial accumulations) only during a few thousand years. 

 He accepts the evidence of comparatively recent glacial action in 

 the higher valleys of North Wales (e. g. near Llyn Ogwen, &c), 

 but enters on no details. 



§ 5. General conclusion. 

 From a review of the facts stated in this paper, combined with 

 the facts stated in a former communication (Nov. 1841*), the au- 

 thor suggests the following classification of the British Palaeozoic 

 rocks. They are considered zoologically as forming one great sys- 

 tem separable into four primary divisions, as follows : — 

 1. Carboniferous, subdivided into four principal groups. 

 («). Magnesian limestone and lower red sandstone, zechstein and 

 rothe-todte-liegende. In this group are the drifted coal plants of 

 the lower red sandstone of England, and the coal-beds of the 

 Hartz, associated with the rothe-todte-liegende. 

 (b). Great coal formations of England, Scotland, Belgium, "West- 

 phalia, &c, freshwater beds, and many beds of plants not far 

 drifted ; sometimes unmoved from the spots where they grew. 

 (c). Millstone grit and shale, limestone, &c, with drifted plants 

 and beds of coal ; great scar limestone ; culm-measures of 

 Devon (?) ; great coal-fields in the West of Ireland, 

 (rf). Lower limestone and limestone shale, &c. ; imperfectly re- 

 presented in England, but probably here and there replaced by 

 the conglomerates at the top of the old red sandstone ; lower 

 limestone and carboniferous slates of Ireland ; lower coal for- 

 mations of Scotland. In this group are placed a part of the beds 

 of North Devon under the culm- measures, and containing fossils 

 like those of the carboniferous slates of Ireland. 

 2nd Division. — Devonian and old red sandstone. In this division 

 are placed the older fossiliferous slates, &c. of Devon and Corn- 

 wall ; the beds below the carboniferous limestone of Belgium and 

 Westphalia, as far as the Eifel and great Westphalian limestones in- 

 clusive ; all the old red fish-beds, &c. of Scotland ; all the central 

 part of the old red sandstone series of Herefordshire ; old red sand- 

 stone, &c. of Ireland. 



3rd Division. — All the Upper Silurian rocks of Mr. Murchison, 

 from the Wenlock slates to the lower part of the " tilestone" inclu- 

 sive ; Denbigh flagstone ; upper division of the fossiliferous slates of 

 Westmoreland and Lancashire ; many portions of the fossiliferous 

 rocks of the Flemish provinces, and various parts of France ; some 

 small fossiliferous groups in the south of Scotland (?) ; a part of 

 the fossiliferous series in the north and south of Ireland (?). 



4th Division. — Great protozoic group ; all the older fossiliferous 

 slates of North and South Wales ; Coniston limestone ; lower part of 

 the " Silurian system" of Mr. Murchison; oldest fossiliferous slates 

 of Scotland and Ireland, and of various parts of the continent, &c. 



* Or Phil. Mag. S. 3. vol. xxi. p. 141. 

 Phil. Mag. S. 3. Vol. 24. No. 159. April 1844. S 



