Page:A Treatise on Geology, volume 1.djvu/171

and clay with calcareous nodules constitute a fish-bed. Thick masses of conglomerate; the basis red sandstone, the imbedded pebbles of various, often great size, derived from the neighbouring mountains.

Pterichthys and Coccosteus are among the characteristic fishes of the lower part of the old red.^[1]

On the borders of the English Lake district we have this combination reduced to a small thickness, and deprived of its upper term. The best sections are seen about the foot of Ulswater, in valleys near Kendal, and at Kirkby Lonsdale. At this latter place we have

Red and light coloured clays with some concretionary limestone (cornstone) resting on

Conglomerate of pebbles derived from the older Silurian strata, which appear higher up on the sides of the valley.

A little further to the S.S.E. the old red series is totally deficient (Craven), and nearly so in Flintshire.

A second combination of the similar elements appears on the border of Wales, and acquires distinctness in the region south of Shrewsbury. An excellent general section is obtained in the country between Dean Forest and the Silurian Vale of Usk. It may be thus expressed^[2]:—

Upper part.—Conglomerate of quartz pebbles and some other fragments, imbedded in red, purple or greenish sandstone. (Holoptychius occurs here.)

Middle part.—Thick laminated red sandstones, with thin marls and some corn stones. (Cephalaspis occurs here.)

Lower parts.—Thick red marls, with greenish bands and blotches, and irregular masses of corn stone. At the base, beds of sandstone gradually passing into or alternating with the top of the upper Ludlow formation.

In all the strata enumerated, and in all their localities, the rarity of in vertebral remains and of vegetable fragments is remarkable. Only a small number of bivalves (not brachiopoda, possibly freshwater shells,) has occurred to Mr. Miller in Scotland. Fishes have

1. Miller's Old Red Sandstone.
2. See Murchison's Silurian System for a full account (the earliest) of the old red in these districts.