UPPER LUDLOW ROCK. 



199 



any at Ludford, have been found near Richard's Castle ; and there is every reason to 

 believe that it extends through various parts of the Ludlow promontory. Nearly all 

 the organic remains found in this singular little bed are figured in PL 4., and the spe- 

 cific characters of the ichthyolite, to which many of them belong, are described in the 

 subsequent pages by M. Agassiz. The coprolites will be also described in the same 

 place. Of these bodies, I would here only observe, that their form, colour, and asso- 

 ciation with fish-bones, naturally led to the opinion of their origin, which has been com- 

 pletely established by the analysis of Dr. Prout. 



4. Fucoid Bed. This bed of greenish grey, argillaceous Sandstone is almost entirely made 

 up of a multitude of small, wavy, rounded, stem-like forms, which so completely re- 

 semble entangled sea-weed, as to induce the conjecture, that tbey must be the impressions 

 of such vegetables. The fucoid bed is also distinguished by containing what are supposed 

 to be columns of some soft zoophyte. They are frequently found in positions which seem 

 to throw light upon the mode of their interment ; for the columns, occasionally some inches 

 in length, are often found in vertical positions, and so standing up surrounded by the fine 

 lamina? of the rock as to suggest the idea that whilst the lower part of the animal was at- 

 tached, the sediment accumulated around the stem l . (See wood-cut below.) 



The columns of this zoophyte are often found on the faces of the highly inclined and vertical 

 joints which so prevail in the Ludlow formation, and which will be described hereafter. Most of 

 these remains occurring just below the bone bed, and the harder portions of them being often found 

 in the fossil fasces of the fishes, we are thus furnished with an additional argument in favour of the 

 belief, that the zoophytes may have been in their natural positions, while the fishes fed upon their 

 edible parts, occasionally swallowing portions of the harder columns of the animal, such as are now 

 occasionally found in the centre of the coprolites. 



Whatever value may be attached to these conjectures, the disposition of the animal 

 remains, when coupled with the finely levigated nature of the inclosing sediment, tend 

 at all events to sanction the belief, that the period of the accumulation must have been 

 one of great tranquillity. Remains of analogous animals and portions of true Crinoidea, 

 have been detected in other layers of the formation, but they are most abundant in and 

 about the fucoid bed. 



1 The copper-plates in which the organic remains of this formation are represented, being filled with figures 

 of other forms, and these fossils having been accidentally omitted, I offer a rough sketch of them in this wood- 

 cut. A further account will appear in the chapter on the organic remains of the formation. 



23. 



2b 2 



