frech's scheme op relationships 255 



Freeh* gives the following scheme showing the relation of the non- 

 marine Old Red sandstone to the normal marine Devonian : 



"Non-marine development. Marine development. 



tt au d j ^ + ~ f Lower Carboniferous, in part. 



Upper Old Red sandstone = | Upper Devonian< 



Land condition and transgression = Middle Devonian. 

 [There is no middle Old Red sandstone. The interval is indicated by a great 

 discordance.] 



Lower Old Red sandstone = \ *f™ Jf °. nian : 



t Upper Silurian, m part. 



These citations make it clear that in Wales and England a series of 

 red marls and sandstones set in near the close of the Siluric, and con- 

 tinued without change through the Devonic into the Lower Carbonic 

 period. During the deposition of 10,000 feet of Old Red sandstone 

 strata no normal marine fauna occurs, and the best criterion for time 

 sequence is therefore absent. 



In Devon and Cornwall there is another series of Devonian rocks, and 

 as these bear normal marine faunas they represent the type area for the 

 Devonic system. However, it is only in recent years that the small 

 English Lower Devonic faunas have become somewhat known. For 

 this reason it was long ago recognized that the Devonic system could be 

 studied to better advantage in the Rhineland. 



" The Devonian system was founded upon one of the most unfavorable and in- 

 complete developments of that series of rocks and faunas known in any part of 

 the globe ; a more precise scope was given to it by the work of its founders, 

 Murchison and Sedgwick, in the Rhineland, but even there no determination of 

 its lower limit was made. This admitted hiatus in the typical succession of De- 

 vonian to Silurian is the parent of the prolific discussions over 'post-Silurian' and 

 ' Hercynian ' faunas." f 



Of the Devonic of Rhineland, Kayser,J one of the leading students of 

 the German Devonic, writes as follows : 



Murchison and Sedgwick "first broke ground on the continent in the Rhenish 

 Schiefergebirge and their westerly extension, the Ardennes, the largest and best 

 developed Devonian area of western Europe, which even up to the present day 

 continues to add more to our knowledge of the Devonian than any other [European] 

 area. 



"The famous essay of the two English observers devoted to the Rhenish moun- 

 tains appeared in 1842,$ and its value was enhanced by the paleontological appendix 



* Lethsea geognostica, 1 Theil, 2 Band, 1897, p. 118. 



f Clarke, in a l'eview of the work cited, American Geologist, vol. xiv, 1804, p. 119. 

 J Text-book of Comparative Geology, by E. Kayser, translated by Philip Lake, London, 1893, 

 pp. 89-91. 

 § Trans. Geol Soc, 2d ser., vol. vi, p. 222. 



