Page:The Habitat of the Eurypterida.djvu/184

176 occur in the top of the series and are succeeded by the Carmylie beds, about 1000 feet thick, of compact red or grey sandstones with some flags, which are the Acanthodian beds described by Goodchild and which contain the abundant fish and eurypterid remains. This series, together with the contemporaneous lavas, forms the backbone of the Sidlaw Hills. It grades up into the Cairnconnan series of 2000 feet of dull red or grey grit with bands of conglomerate. The succeeding Red Head series, 1500 feet thick, consists in the lower part of "fine red thin-bedded sandstone with bands of hard bright red shale, while the upper portion is made up of thicker-bedded sandstone." Six or seven miles south of the Red Head promontory from which the beds are named, there is a lithological change to blue or grey shales with sandstone partings, illustrating well the rapid lateral variation. Overlying this group is the Auchmithie conglomerate. "The series consists of three main masses of conglomerate, with intervening sandstones and conglomerates. The pebbles in the conglomerates are well rounded, fairly large (generally 1 to 6 inches, rarely 12 inches), and, as usual, are mostly quartzite" (117, 400). This conglomerate is 800 feet thick and is followed by the highest member of the series, the Arbroath sandstone (1200 feet). "Coarse, gritty sometimes pebbly sandstone is its component rock, always red in color" (117 400). The succession as here shown in Forfarshire shows beyond a doubt that the sediments could not have been marine. The complete series is shown in outcrops in Forfarshire, extending over about 500 square miles, while within a distance of less than ten miles the outcrops of all of the formations may be seen.

The Orcadian. Over the greater part of northeast Scotland and extending northward to the Orkney and Shetland Islands there is developed a great series of flags, sandstones and conglomerates younger in age than the Caledonian and these have been called the Orcadian by Goodchild. They constitute the Lower Old Red as used by Geikie and were thought by him to have been deposited in the large water body which he called Lake Orcadie. Neither the natural base nor top of the series has been seen and even the highest members are always followed unconformably by the Upper Old Red. It is unnecessary to take up the formations in detail because they do not contain eurypterids. There are three fossil horizons containing, with one exception, only fish remains. These horizons are the Achanarras beds, the Thurso flags and John o'Groats flags.

Goodchild in summarizing the conditions which obtained in