Chap. IV.] 
THE CARADOC FORMATION, 
63 
CHAPTEE IY. 
LOWER SILURIAN ROCKS {continued). 
THE CARADOC FORMATION. — SHELLY SANDSTONES OF CAER CARADOC. — GENERAL CHARACTER 
AND ORDJIR IN THE TYPICAL SILURIAN TRACT OF SHROPSHIRE. — CHIEF ORGANIC REMAINS 
AS DISTINGUISHED FROM THOSE OF THE LLANDE1LO FORMATION. GREAT MASSES OF THE 
SLATY ROCKS OF WALES, INCLUDING THE BALA LIMESTONE, SHOWN TO BE THE EQUIVA- 
LENTS OF THE CARADOC OF SHROPSHIRE. IGNEOUS ROCKS, COTEMPORANEOUS AND ERUP- 
TIVE, OF LOWER SILURIAN AGE. 
That certain sandstones and shales with occasional calcareous or shelly 
courses overlie the schistose rocks of the Llandeilo formation in "Wales, has 
already been indicated *. But before we pursue their clear and consecutive 
relations, let us view those masses of the same age in Shropshire, which, with 
their fossils, were originally described as a formation younger than the 
Llandeilo flags, and as underlying all the Upper Silurian rocks. For, 
this Caradoc formation and its characteristic fossils having been described 
and named many years before its equivalents in Wales were brought into 
comparison or their fossils examined, the account of the original type 
naturally precedes any description of strata subsequently ascertained to be 
of the same age. 
In Shropshire, the Caradoc Sandstone, so named from the ridge on the 
flanks of which it is well exposed, is cut off, as formerly shown, from the 
next deposits below it, namely the Llandeilo flags, by the intervention of 
the Cambrian rocks of the Longmynd (see Map). Whilst a perfectly sym- 
metrical ascending order occurs, as already stated, on the west flank of the 
Longmynd, from the Cambrian into the lowest of the Silurian rocks, and 
from them into the Llandeilo formation, in vain do we look on the eastern 
side of that mountain for any representative of the Stiper Stones and 
the great Llandeilo formation of the Shelve and Corndon tract (p. 38). 
The steep slopes of the Longmynd which overhang the valley of Church 
Stretton exhibit, as already shown (p. 26), the escarpment of the lowest 
beds of that enormous mass of ancient sedimentary rocks. (See Map.) 
Immediately to the east of that valley is seen the line of a powerful 
fault, the vertical dimensions of which have been estimated (by Professor 
Eamsay) at not less than 2000 feet, the place of the intervening strata 
being taken by igneous rocks. The latter having been erupted at a period 
long after the formation of the original sediments, have altered the schists 
into hard clay-slates, and the sandstones into quartz-rock. These igneous 
* See also general section beneath Map, and local sections (pp. 55 & 60). 
