J. Pringle — Lower Tremadoc Rocks, Si. David's. 557 



and are brought against shales belonging to the zone of Diclymograptus 

 extensus. The series is not well exposed inland, but is seen to 

 advantage in the cliff at the north end of the island. 



The lowest beds of the group are thin grey sandstones with some 

 shales. Hicks regai'ded them as forming the base of the ' Tremadoc ', 

 and they extend along the foot of the cliff on the west side of Ogof 

 Velvet. They are succeeded by grey sandy shales with thin lenticles 

 of sandstone, and these in turn are overlain by bluish-grey iron- 

 stained mudstones, which are highly fossiliferous. It was from 

 the latter that Hicks obtained his fossils. The strata, which are 

 about 1,000 feet thick, have an average dip of about 60°, and they 

 strike from N.E. to S.W. 



Trwyrv Shorv Owen, 



Ogof Velvet 



Trwyrt, 

 OgofMetv 



'Tocf^v 



lArijgitla, 

 Flags 



LV TrerrvaxLoa 

 ofDVHlchs 



D.EocterhSUus 

 JB&cbs 



Sketch-map 1 of the north-eastern portion of Eamsey Island. Scale, 6 inches 

 to 1 mile. Vertical shading indicates Lingula Flags ; horizontal shading 

 indicates Lower Tremadoc of Dr. Hicks ; cross - hatching indicates 

 Didymograptus extensus beds. Fossil localities shown thus : Al, A. 2, etc. 

 Thick lines represent faults. 



Hicks and Salter 2 believed that the ' Tremadoc ' rested conformably 

 on the Lingula Flags, and that the latter gradually passed upwards 

 into the former group. They were clearly in error, however, as 

 the junction proves to be faulted. The line of dislocation, which 

 runs nearly parallel with the strike, can be seen descending the 

 cliff above Ogof Velvet. The detection of this fault greatly simplified 



1 The line-drawing from which this illustration was prepared was kindly- 

 made by Mr. E. Ashborn. 



2 Hicks & Salter, Second Eeport on the Menevian Group and other 

 formations at St. David's, Pembrokeshire : Eep. Brit. Assoc, Nottingham, 

 1866, p. 184. 



