alternating sedimentary and igneous rocks which were contemporaneous in their development with the main volcanic outpourings (see sketch map, fig. 17).
The first important fossiliferous beds are those found at Carmylie and adjoining localities in Forfar. These constitute a part of the famous Arbroath flags and because of their abundant eurypterid
 Fig. 17. Sketch Map of Scotland, Showing Localities where Old Red Sandstone Outcrops |
remains are called the Pterygotus beds. In them are found the most perfect specimens of Pterygotus anglicus, though complete individuals are rare, and the rock often contains also an abundance of Parka decipiens, which has been variously identified as crustacean egg cases and as spores of plants. Above these beds follows the main mass of the lavas upon which rest the beds of Auchtertyre, which
