Chap. VII. 
UPPEE LUDLOW ROCKS. 
133 
Orthocerata, occasionally of large size, occur, the species being the same as those 
known also in the Lower Ludlow rock, PL XXVI. et seq. 0. bullaturn abounds. 
Of Trilobites, Phacops caudatus and Encrinurus punctatus, with a rare sample of 
the Calymene Blumenbachii, reach the summit ; but they are not abundant. The 
most prevalent Trilobite is a fine species of the genus Homalonotus (H. Knightii, 
PL XIX. f. 7), which may be found throughout the whole range of this formation, 
from Pembrokeshire to Westmoreland, and is sometimes of very large size. 
In the cliffs at Ludlow, the chief body of rock is surmounted by what has 
been termed the Fucoid-bed. This is a greenish-grey, argillaceous sandstone, 
almost entirely made up of a multitude of small, wavy, cylindrical, stem-like 
forms which resemble entangled Sea-weeds. In this mass is found, and always 
in a vertical position, the singular body (PL XII. f. 5) named Cophinus dubius. 
It is generally of an inversely pyramidal shape, and its sides are scored with 
elegant transverse grooves. I am assured by Messrs. J. De C. Sowerby and Salter, 
who have studied it attentively, that it is the impression made by the stems of 
Encrinites, which, rooted and half-buried in the micaceous mud, have produced, 
by their wavy and somewhat rotatory motion, the beautiful pattern, every line 
of- which answers to one of the projecting bosses or rings of the jointed stem. 
In fact these stems are always found lying contiguous to the markings. Such 
bodies, in their slow trailings or gyrations, may have probably left accurate im- 
pressions, in consequence of the diffusion of small particles of mica in the mud, 
the flat plates of which, having been drawn into positions parallel to the line of 
motion, may have impeded the perfect fusion of the separated portions of the 
semifluid mass after the stem had passed through them. 
The highest member of the Ludlow rocks is most interesting, inasmuch 
as until recently it was described by myself as being the oldest rock in 
which fossil Eishes had been found. The only exception is that already 
alluded to — the occurrence of a fragment of Pteraspis in the central part 
of this same formation. The uppermost Ludlow rock also contains the 
earliest remains of Land Plants (see pp. 135, 138). The lower layers of 
this zone, as seen at Ludlow, are finely laminated, earthy, greenish- 
grey sandstones, containing a few Ichthyolites, with several shelly re- 
mains characteristic of the formation. It was the middle part only of 
this band, or a gingerbread- coloured layer of a thickness of three or four 
inches, and dwindling away to a quarter of an inch, which exhibited, 
when my attention was first directed to it *, a matted mass of bony frag- 
ments, for the most part of small size and of very peculiar character. 
These, with a few remains of Shells and Crustaceans, including Pterygotus 
problematicus, occur in a cement in which varying proportions of carbo- 
nate of lime, phosphate of lime, iron -oxide, and bitumen are disseminated. 
Some of the fragments of Eish are of a mahogany hue ; but others are of so 
brilliant a black that, when first discovered, they conveyed the impression 
* This course was discovered by my friends which might be considered to pertain to Fishes, 
and excellent Ludlow coadjutors, the Eev. T. T. These he affixed to tablets, which I believed to 
Lewis and Dr. Lloyd, both now, alas ! removed have been deposited with the original Silurian 
by death. By their assistance, and that of the types presented by myself to the Museum of the 
late Eev. W. E. Evans, I traced this fish-bed in Geological Society ; but, unluckily, these unique 
several other parts of the Ludlow promontory, and precious forms, so carefully drawn by Mr- 
See Sil. Syst. pp. 198, 605. Mr. Evans showed James De C. Sowerby, and described by Agassiz 
great sagacity and talent in selecting all the forms (see PI. XXXV.), can now nowhere be found. 
