484 Prof. Sedgwick on the May Hill Sa?ulsto?ie, 



Two of the above {E. punctatus and O. testudinaria) are some- 

 times found in Silurian rocks, the others are exclusively Cambrian. 



2nd. North side of the hill, from an old quarry, and thence 

 down to the level of the river. 



Stenopora fibrosa. 

 Petraia uniserialis* 

 Spirigerina reticularis, 

 Leptagonia depressa. 



Pentamerus oblongus (abundant). 

 — . — linguiferus (including 



undaius). 

 Turrit ella cancellata (?). 



Here we have not one exclusively Cambrian species, but several 

 which are common to Cambrian and Silurian rocks. Like that 

 of Penlan, it is a good May Hill fossil group. 



Such were the results of a single day's examination of the very 

 broken and difficult country to the south of Llandovery. It 

 would, perhaps, have been impossible to arrange its beds in any 

 approximate geological order had there been no clearer evidence 

 in any other typical country. There are, however, in this 

 country two very distinct fossil groups, — a May Hill group, and 

 an upper Bala or Cambrian group. These two groups are in 

 the quarries exhibited apart. They do not appear to alternate 

 or interchange places. They have several species in common, 

 but there is no confusion among the typical species. Thus, no 

 truly characteristic Cambrian species was found in the upper or 

 May Hill beds; and, in like manner, no truly characteristic 

 Upper Silurian or May Hill species was found in the Cambrian 

 beds. Such were the facts observed, whatever be the consequences 

 to which they may lead us. The facts are stated fairly and 

 without reserve. 



VL Section of Castell Craig Gwyddon, ^c. 



For purpose of illustration, I here exhibit a reduced sketch of a 

 small part of two beautiful sections published by the Government 



N.W. 



Fig. 4. 



Castell Craig Gwyddon. 

 Noedd Grug. | 



\ i 



1 . Old Red Sandstone. 



2 and 3. Ludlow and Wenlock. 



4. Probably Wenlock. 



5. May Hill beds of Castell Craig Gwyddon, probably 



continued through Noedd Grug. 



6. Cambrian group, geologically far above the Llan- 



deilo flag in tne valley of the Towy. 



Survey and the author of the ' Silurian System.' Of the general 



