The beds next below the yellow sandstone are well seen in the large zone of Old Red which skirts the southern flank of the Grampians from Stonehaven to the Frith of Clyde. It there forms, together with trap, the Sidlaw Hills and the strata of the valley of Strathmore. A section of this region has been already given ([p. 48.]), extending from the foot of the Grampians in Forfarshire to the sea at Arbroath, a distance of about 20 miles, where the entire series of strata is several thousand feet thick, and may be divided into three principal masses: 1st, and uppermost, red and mottled marls, cornstone, and sandstone (Nos. 1. and 2. of the section); 2d, Conglomerate, often of vast thickness (No. 3. ibid.); 3d, Roofing and paving stone, highly micaceous, and containing a slight admixture of carbonate of lime (No. 4. ibid.). In the first of these divisions, which may be considered as succeeding the yellow sandstone of Fifeshire before mentioned, a gigantic species of fish of the genus Holoptychius has been found at Clashbinnie near Perth. Some scales (see [fig. 395.]) have been seen which measured 3 inches in length by 21/2 in breadth.
At the top of the next division, or immediately under the conglomerate (No. 3. [p. 48.]), there have been found in Forfarshire some remarkable crustaceans, with several fish of the genus named by Agassiz Cephalaspis, or "buckler-headed," from the extraordinary shield which covers the head (see [fig. 396.]), and which has often been mistaken for that of a trilobite, of the division Asaphus.
Fig. 395.
Scale of Holoptychius nobilissimus, Agas. Clashbinnie. Nat. size.
Species of the same genus are considered in England as characteristic of the second or Cornstone division ([p. 343.]).
Fig. 396.
