Ch. XXVII] upper SILURIAN BONE-BED. 431 



ceras buUahcm, Trochus? helicites, Bellerophon trilohatus, Chonetes lata, 

 &c., with mimerous defences of fishes. These beds are well seen at King- 

 ton in Herefordshire, and at Downton Castle near Lndlow, where they 

 are quarried for building. 



b. Gray Sandstone, &c. — The next subdivision of the Upper Ludlow 

 consists of gray calcareous sandstone, or very commonly a micaceous 

 stone, decomposing into soft mud, and contains, besides the shells just 

 quoted, the Lingnla cornea, which is common to it and the Tilestone beds. 

 The Orthis orbicularis, a round variety of 0. elegantula, is characteristic 

 of the Upper Ludlow ; and the lowest or mudstone beds are loaded for a 

 thickness of 30 feet with Athyris navicula (fig. 568). As usual in strata 

 of the Primary periods, the brachiopodous moUusca predominate over the 



Fig. 567. Fig. 568. 



Orthis elegantula, Dalm. Yar. orbicularis, Athyris {Terehratida) navicula, J. Sow. 

 J. Sow. Delbury. Aymestry limestone ; also in 



Upper Ludlow. Upper and Lower Ludlow. 



lamellibranchiate ; but the latter are by no means unrepresented. Among 

 other genera, for example, we observe Avicula (or Pterinea), Carcliola, 

 Nucula, Sanguinolites, and Modiola. 



Some of the Upper Ludlow sandstones are ripple-marked, thus afford- 

 ing evidence of gradual deposition ; and the same may be said of the ac- 

 companying fine argillaceous shales which are of great thickness, and have 

 been provincially named " mudstones." In some of these shales stems of 

 crinoidea are found in an erect position, having evidently become fossil on 

 the spots where they grew at the bottom of the sea. The facility with 

 which these rocks, when exposed to the weather, are resolved into mud, 

 proves that, notwithstanding their antiquity, they are nearly in the state 

 in which they were first thrown down. 



The hone-hed of the Upper Ludlow deserves especial notice as affording 

 the oldest well-authenticated example of the fossil remains of fish. It 

 usually consists of a single thin layer of brown bony fragments near the 

 junction of the Old Red Sandstone and the Ludlow rocks, and was first 

 observed by Sir R. Murchison, near the town of Ludlow, where it is three 

 or four inches thick. It has since been traced to a distance of 45 miles 

 from that point into Gloucestershire and other counties, and is commonly 

 not more than an inch thick. At May Hill two bone-beds were observed, 

 with 14 feet of intervening strata full of Upper Ludlow fossils.* At that 

 point immediately above the upper fish-bed numerous globular bodies 

 were found, which were determined by Dr. Hooker to be the spores of a 

 cryptogamic laud-plant, probably Lycopodiaceous. These beds occur just 



* Murchison's Siluria, pp. 187-23Y. 



