364 Prof. Sedgwick on the May Hill Sandstone, 



The Herefordshire fish-beds (cornstone) I had formerly placed 

 over the Plymouth group, on the understanding that certain 

 supposed fish-beds of Cornwall were probably of the age of the 

 Dartmouth group. As, however, the Cornish fish-beds have 

 disappeared from the sections, I should think it much the safest 

 to place the cornstone group at the base of all the groups of De- 

 vonshire; especially as it seems in some places to pass down- 

 wards into the tilestone of the Ludlow group, and therefore 

 appears to give us (what we do not find in Devon and Cornwall) 

 a base to the Devonian series. In this way we might arrange 

 the several groups in a regular numerical order, and unite them 

 numerically to the Silurian series. But the phsenomenain Scot- 

 land seem to forbid any such intimate union. 



The Petherwin group is provisionally arranged in the Devonian 

 series. Physically, it is best connected with the older groups 

 of Devonshire and Cornwall ; but palceontologically , it is as well 

 connected with the rocks of the Upper Palseozoic division *. 



Devonian Series of Scotland, 

 Grand as is the development of the old red sandstone of Here- 

 fordshire, it dwindles into insignificance when compared with the 

 rocks which pass under the same name in Scotland. They are 

 divided by Miller as follows : — 



1. Great conglomerate and red sandstone. 



2. Bituminous schists — Dipterus, Pterichthys, CoccosteuSy &c. 



3. Red and variegated sandstone. 



[These three groups form the " lower formation," as well seen in 

 Caithness. 



4. Gray sandstone, earthy slates, &c. [This "middle formation" 



contains a peculiar group of fishes, Cephalaspis, &c.] 



5. Red sandstone and conglomerate. 



6. Impure concretionary limestone. 



7. Yellow siliceous sandstone. 



[The last three, called the " upper formation," are characterized by 

 Holoptychius, &c.] 



This vast North-British series has no true palseontological 

 base j but its '' upper formation '' seems to graduate into the 

 carboniferous series. 



Its lower groups have no known representatives in the old 

 red sandstone of Herefordshire, and cannot be drawn into com- 

 parison with the " Tilestone^' and fish-beds of the Ludlow rock. 

 But its middle group and " upper formation '^ are represented, 

 though imperfectly, by the " cornstone '' and overlying conglo- 

 merates, &c. of Herefordshire. 



From the above facts it seems to follow,— (1) that the old 

 red sandstone of Herefordshire and South Wales (spite of its 



* This question is discussed in a naper on the Slate Rocks of Devon and 

 Cornwall, Quarterly Journal of Geol. Soc. vol. viii. 1852. 



