Chap. II.] 
STKUCTUKE OF THE LONGMYND. 
27 
clear idea to the reader of that order which every geologist may examine 
for himself when he walks from the valley of Church Stretton across the 
Longmynd to the well marked ridge of the Stiper Stones, and thence into 
that typical Lower Silurian tract of the Shelve and Corndon district, which 
will presently he illustrated. 
A second diagram, reduced by Mr. Aveline from one of the published 
large sections of the Geological Survey, and which will appear in the next 
Chapter, is a satisfactory confirmation of the views which, broached in 
1833*, were reiterated in 1835 f (when the term Silurian was first applied 
to all the strata overlying the Longmynd), and were finally and fully 
developed, with coloured illustrations, when the Silurian System' was 
published J. 
In the ' Silurian System/ as well as in Memoirs published some 
years previously by the Geological Society, I described the Longmynd 
rocks in detail, and showed that, besides the strata of mechanical and 
aqueous origin, there are associated with them greenstones and other 
intrusive rocks, which had in part altered the deposits they penetrated. 
It was further stated that some of the altered rocks contained copper 
veins, and that others had cavities lined with crystals of quartz, and occa- 
sionally with bitumen or mineral pitch §. The exudation also of mineral 
pitch from rocks of the same age and character, both at Haughmond Hill 
to the north of Shrewsbury, and at Pitchford to the east of that town, was 
pointed out, as well as the frequent recurrence of thin strings of copper- 
ore. 
The geologist will naturally attach much interest to the occurrence of 
occasional flakes of anthracite in these very ancient strata, and to their 
yielding petroleum. For if these substances were formed out of vegetable 
or animal matter, we can refer to little else than Seaweeds or Annelides 
as their sources ||. 
Neither in the period extending from 1831 to 1835, during which I 
first explored them, nor in subsequent years, when searched by the Geo- 
logical Surveyors, up to the time when the first edition of this volume was 
published (1854), had any traces of organic remains been discovered in 
these Longmynd rocks ; and hence, whilst their position and mineral cha- 
racters were described, they were still spoken of as ' unfossiliferous,' or as 
* Proc. Geol. Soe. vol. i. p. 475. his mind on this subject, the reader may consult 
t Phil. Mag. & Ann. of Ph. 1835, p. 46. with advantage a memoir by M. Abich, in the 
I The 'Silurian System' was really issued in Acad. Sc. St.-Pe'tersbourg Bull. Phys.-Math. torn. 
1838, though 1839 is on the title-page. In proof of xiv. nos. 4 & 5, in which the author, insisting upon 
this, see Lyell's Elements of Geology, 1838, in the intimate connexion between the gases pro- 
which the leading data of the Silurian System are ceeding from mud-volcanos and other volcanic 
quoted from my work. outbursts, dwells on the close geological affinity 
§ The manner in which certain cavities of these existing between all such operations, including 
rocks are filled with bitumen and small patches of hot springs, &c, and the different sorts of bitu- 
anthracite (Sil. Syst. pp. 260, 265 et seq.% and also men, asphalt, &c. M. Abich views petroleum 
the veins of copper-ores which they contain near (like that which issues from the rocks of Pitch- 
the junction of the intrusive rocks, are facts ford and Haughmond Hill : see diagram, Sil. Syst. 
worthy of attention. p. 265) as a compound primitive body engendered 
|| The origin of the bitumen exuding from the in the interior of the globe, whence it rises like 
interior of these very ancient deposits is neces- carbonic acid, of which the real origin is also un- 
sarily most difficult of explanation. To satisfy known. 
