Chap. V.] 
UPPER LLANDOVERY ROCKS. 
80 
ir 
O 3 
O 
§3 
0 H as liljlk ^ Lower Silurian forms, and had never de- 
1 m If© ^§ HI tected it in the overlying Wenlock shale, 
5 ^ | H| and, further, as in the greater part of the 
^ £6 H Silurian territory the strata which con- 
% |« tain it are coarse grits and sandstones 
N H 2 resembling the inferior rocks, but wholly 
^ H J3 unlike the superior argillaceous formations 
rS of Shropshire and Herefordshire, I naturally 
classed the rock with the Lower Silurian. 
^ Many years elapsed, and even the Geo- 
M - logical Surveyors also examined and mapped 
^ ^ , ^ % the district under consideration without 
| ■§) perceiving the break; but it was detected 
> in 1853 by the researches of Messrs. Aveline 
1 and Salter (Quart. Journ. Geol. Soc. vol. x. 
| §o jjjjfjaj! P p- 62). These gentlemen observed a want of 
|L conformity between the great mass of the so- 
P called Caradoc sandstone beneath and the 
* rocks with Pentamerus above, the latter 
^ liB § being perfectly conformable to the Wenlock 
Iffl^B 1 shale. The amount of unconformity, as seen 
J in this woodcut, which is taken from apub- 
§ lished section of the Government Survey, is 
^ I 18918 2 greater than that which can be detected on 
^, Q the line near Wistanstow, on which the suc- 
°° Sll^ ^ cession was originally noted by myself*. 
J This diagram exhibits not only the Upper 
2 Llandovery rock reposing in one place upon 
.§ the truncated edges of the Cambrian or 
"fj Longmynd rocks, a, and in another place 
3 o " 6 transgressive on the true Caradoc, c, but is 
0 § B^p ° further highly expressive of the powerful 
1 S Bills ^ fractures or faults by which the typical 
^ i Jfll&z3 I 3 region has been affected at periods long 
3 subsequent to all those movements of the 
6 jfciE^S 53 subsoil which produced the unconformable 
g 53 deposition of these strata. 
When this country was examined by me 
in 1832-3-4, it was, indeed, considered 
that the powerful outbursts of igneous 
^ J ~* matter, seen in the contiguous eruptive 
Ph ft M 
* The amount of this discordance on the Onny can only with 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 times the 
point of junction are so overhanging, that the river must be waded to see the break, 
slightly transgressive arrangement of the strata 
p " 00 
m - <o 
5 p m 
