2. Forming an outer zone or rampart, and overlapping the conglomerate, a gray fossiliferous sandstone constitutes the next member of the Devonian group. This deposit is widely extended, and consists of several beds. One of these is a fine-grained, compact building stone. Another, the well-known flag-stone, is of a more slaty texture, of a dark-blue color, and abounds in mica. These sandstones occupy a great part of the sea-ward barrier by Montrose, Arbroath, and the high grounds of Carmylie. They fold over the Sidlaws on both acclivities of the range, where they form a well defined example of what geologists term the _anticlinal_ and _synclinal_ axes, that is, the rock curves and reduplicates, like a soft flexible substance, according to the undulations of the surface. The several beds cross the Tay in the direction of Dundee, and emerge on the opposite banks at Wormit-bay, Parkhill, and Newburgh; ranging eastward along the northern slope of the Ochils by Norman’s Law and the high table-land of Balmerino. 3. A limestone rock, termed CORNSTONE, from its practical application to grinding purposes in England, occupies a place among the old red sandstone series. This deposit occurs in thin bands of a dull yellowish or blue-colored stone, containing numerous cherty nodules, and, where compact, is of a sub-crystalline texture. The cornstone generally contains more of silicious than of calcareous matter, and is consequently not much prized for building or agricultural purposes. In Scotland no organisms have been as yet detected in it, but in England it yields abundantly remains of the cephalaspis and various crustaceans. This rock is not co-extensive with the other members of the group, nor do we find it continuous in any part of the district which it occupies. It is generally found in small detached patches, as at Glen-Finlay, Meigle, Cargill, on the north of the Sidlaws; at Ballendean, Rait, Meurie, in the Carse of Gowrie; at Parkhill, Newburgh, Clunie, Kinnaird, on the south bank of the Tay; and at Newton and Craigfoodie, on the southern face of the Ochils. At the Newburgh station of the Edinburgh and Northern Railway the cornstone is inclosed among the eruptive rocks, partaking of their common induration, and, except in its distinct lamination, cannot be distinguished in color or texture from the traps.