Siluria : a history of the oldest rocks in the British Isles and other countries with sketches of the origin and distribution of native gold, the general succession of geological formations, and changes of the earth's surface / by Sir Roderick Impey Murchison.

Roderick Murchison, 1st Baronet

Date:: 1867

Credit: Siluria : a history of the oldest rocks in the British Isles and other countries with sketches of the origin and distribution of native gold, the general succession of geological formations, and changes of the earth's surface / by Sir Roderick Impey Murchison. Source: Wellcome Collection.

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$o H O O W MH H P **) cd 0) be «<s ■g» o 2 •-H C2 <1/ S—/ l^i J'- O « c t- u O 3 § 02 'a s -So 8 g o H CO W CO ” 03 O ^ o o S g m Q 5 2 .2 £i w o Cm HH p ^ 03 -* F S O -C U o W [V] V. m r' P o w 03 (3 Q u: i-3 o « >- o PS O w > '^s o W F Ei Y. ►J PS w p. Ph p w p o 03 5P O w p 00 ii O o XI o P U !2 O Lower Silurian forms, and had never de- tected it in the overlying Wcnlock shale, and, further, as in the greater part of the Silurian territory the strata which con- tain it are coarse grits and sandstones resembling the inferior rocks, hut wholly unlike the superior argillaceous formations of Shropshire and Herefordshire, I naturally classed the rock with the Lower Silurian. Many years elapsed, and even the Geo- logical Surveyors also examined and mapped the district under consideration without perceiving the break; hut it was detected ill 1853 by the researches of Messrs. Aveline and Salter (Quart. Journ. Geol. Soc. vol. x. p. 02). These gentlemen observed a want of conformity between the great mass of the so- called Caradoc sandstone beneath and the rocks with Pentamerus above, the latter being perfectly conformable to the AVcnlock shale. The amount of unconformity, as seen in this w'oodcut, which is taken from a pub- lished section of the Government Survev, is greater than that which can he detected on the line near AVistanstow, on which the suc- cession Avas originally noted by my.self This diagram exhibits not only the Upper Llandovery rock reposing in one place upon the truncated edges of the Cambrian or Longmynd rocks, a, and in another jilacc transgressive on the true Caradoc, c, but is further highly expressive of the powerful fractures or faults by Avhich the typical region has been aftected at periods long subsequent to all those movements of the subsoil Avhich produced the unconformahlc deposition of these strata. AVhen this country Avas examined by me in 1832-3-4, it was, indeed, considered that the poAverful outbursts of igneous matter, seen in the contiguous eruptive * The amount of this discordance on the Onny can only Avith great difficulty be ascertained, and is so slight, and the banks of the river at the that when the river is very low; at other^imes the point of junction are so overhanging, that the river must be waded to see the break, slightly ti’ansgressive arrangement of the strata$