Memoirs of the Geological Survey of England and Wales. ..., Volume 3H.M. Stationery Office, 1881 |
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Autres éditions - Tout afficher
Memoirs of the Geological Survey of England and Wales. ..., Volume 2,Partie 2 Geological Survey of Great Britain Affichage du livre entier - 1848 |
Memoirs of the Geological Survey of England and Wales. ... Geological Survey of Great Britain Affichage du livre entier - 1846 |
Memoirs of the Geological Survey of England and Wales. ... Geological Survey of Great Britain Affichage du livre entier - 1846 |
Expressions et termes fréquents
angles Anglesey anticlinal Aran Arenig Arenig beds Arenig slates ash bed ashy Bala beds Bala Lake Bala limestone bands Cader Idris Caernarvonshire calcareous Cambrian Cambrian grits Cambrian rocks Caradoc cleavage conglomerate contorted Conwy curve Dalm David's Denbighshire denudation Dolgelli Dolwyddelan east fault feet felspar felspathic felspathic ashes felspathic porphyry felstone Ffestiniog foliated fossiliferous fossils Geol glabella greenstone grey Hicks hills igneous rocks interstratified Journ Lingula beds Lingula flags Lingulella Llanberis Llandeilo Llandovery Llyn Llyn Padarn Lower Silurian M'Coy mass Menevian Merionethshire metamorphic miles Moel Moel Hebog Mowddwy Mynydd neighbourhood North Wales north-east north-west Orthis overlying pass porphyry quarries quartz Ramsey Island Red Sandstone Salt Salter shale side Silurian Silurian rocks Silurian strata slaty beds Snowdon south-east south-west species strata strike Tarannon shale thick thin Tremadoc Tremadoc slates unconformably valley volcanic Wenlock
Fréquemment cités
Page 173 - of porcellanite into the condition of that kind of absolute fusion that in many other regions seems to have resulted in the formation of granites, syenites, and other rocks, commonly called intrusive. This conclusion is further aided by the capricious variation in thickness of the strata adjoining the
Page 333 - And as the element of depth is found in modern seas to be of more importance than the condition of the sea bottom, it is not to be wondered at that there should be a great similarity between the two districts. The typical Caradoc is unquestionably a shallow-water deposit. It
Page 173 - the river Ogwen. So closely does the matrix of the altered rock resemble the adjoining typical porphyry in colour, texture, and even in porphyritic character, and by such insensible gradations do they melt into each other, that the suspicion or rather the conviction constantly recurs to the
Page 176 - it is impossible to define any line of demarcation between conglomerate and porphyry, for, among other reasons, though the strata as a whole undulate to the south-east at low angles on the south bank of Llyn Padarn, yet the last dip is towards the porphyry, evidently without a fault.
Page 173 - The best sections are in the Passes of Llanberis and Nant Francon, where the succession of the strata, as a whole, is as follows :—The highest beds consist of about 1,300 feet of green, greenish grey, and occasionally of purple hard grits, generally thick-bedded, and formed of grains of quartz often but little waterworn, intermingled
Page 330 - east, and even in the mountain land from Cader Idris to the Menai straits, traces of a similar approximate uniformity of height are plain to the experienced eye, showing the relics of an old form of ground, in which deep valleys have been not rent but scooped out. In lower ground, the features of Denbighshire
Page 316 - and never could have been any other possible outlet for the water of the lake than the channel of the Dee, it is quite certain that it lies in a rock-bound basin; and, indeed, it seems to me more than likely that the large alluvial flat more than six miles in length between
Page 306 - The whole country in fact is intersected by valleys so numerous and comparatively so steep on the sides that there is scarcely any part of Wales more difficult of access than this part of Denbighshire. It is essentially a rural district, without large rivers, without
Page 19 - cases to the original angularity of its component grains, and in others to the partial effect of what is termed metamorphic action. The beds seemed to have been formed partly by the direct waste of rocks of a granitic character, or at least into the composition of which quartz and
Page 329 - nothing more striking than the average flatness of the tops of many of the hills, especially when the rocks which compose them are of tolerably uniform texture ; a flatness, be it remembered, not connected with anything like a horizontal position in the beds, for everywhere they are contorted and often stand on end. All Wales shows this feature, from the Towey