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172 The Lanarkian Rocks (Downtonians of the Geological Survey, the original Lower Old Red of earlier writers).

Ludlow Rocks.

Mr. George Hickling who has made a special study of the Lower Old Red in Forfarshire, where it is typically developed, has given a somewhat different tabulation (117, 398):

The employment of different names for deposits perhaps synchronous, but occurring in different localities, is inevitable because of the lack of stratigraphical continuity and because the fossils which are found in these rocks are not of the type to serve as good index fossils, if, as I hope to show, they lived in the rivers.

It will not be possible to work out the lithogenesis of the eurypterid-bearing beds in the Old Red by a study of those beds alone; rather must we take a broader view that will lead to an interpretation of the climatic and other physical conditions which obtained throughout the Devonic in the regions where red sedimentation was going on. Having determined what these conditions were, the origin of the sediments, the agents of transportation and especially the nature of the areas in which deposition occurred, i.e. whether under water or on the land, then the character of the faunas and of the restricted beds in which they occur, will automatically be ascertained. A few detailed sections in the type localities will enable us to generalize later on.

The Caledonian. At the end of the Siluric there was a period of folding and erosion, the extent of which is not known, but most of the sections indicate that it was long, and perhaps nowhere has a true gradational contact been found between the uppermost Siluric and the lower Old Red. Goodchild remarks in this connection, "So far from graduating downward into the Silurian rocks, the local base of the formations under notice (the Caledonian) lies with a violent unconformity upon all of these rocks, and may repose indifferently