172 THE HABITAT OF THE EURYPTERIDA 



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): 



Feel 



Edzell shales 1,000 



Arbroath sandstone 1,200 



Auchmithie conglomerate 800 



Red Head series 1,500 



Cairnconnon series 2,000 



CarmyUie series 1,000 



Dunnottar conglomerate 5,000 



12,500 



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 euryp- 

 terid-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 interpreta- 

 tion 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 ascer- 

 tained. 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 



