1872.] 



HICKS- — TREMADOC ROCKS. 



41 



stratified with grey flaky slate containing LinguleUa Davisii in great 

 abundance. They graduate by almost insensible degrees from these 

 as hard grey flags, then bluish grey, with some thick-bedded rock of 

 tough texture. They have a thickness of nearly 1000 feet, with an 

 average dip of about 60°, and the strike of the beds is from N.E. to 

 S.W. They form the north-east point of the island, and are exposed 

 in an excellent coast-section, with the Lingula-fiags dipping under 

 them, and the dark iron-stained Arenig slates resting upon them. 

 It is doubtful, however, whether the latter rest conformably upon 

 them. I am inclined to think that a fault intervenes, and that the 

 proper thickness, as shown at some of the other places, does not 

 occur here in consequence. 



Fig. 2. — Section across the northern part of Ramsey Island (see Map). 



W. Fault. E. 



5. Lingula-flags. 



6. Tremadoc rocks. 



7. Arenig rocks. 



At "Whitesand Bay they also rest conformably on Lingula-flags ; 

 but a fault running up in a north-east direction, and almost in the 

 strike of the beds, has removed more than three fourths of their 

 thickness, and has brought down the Arenig group in contact with 

 them, so as to give it an appearance of resting almost conformably 

 upon them. Further north, near Llanveran, the fault has gone 

 eastward of the series, and they are seen again in nearly their entire 

 thickness underlying the Arenig group. 



The third patch, at Tremanhire, in the middle of the country, 

 east of St. David's, occupies a greater area ; but there are only a 

 few quarries open, and therefore considerable difficulty has been 

 experienced in defining its proper limits. The Lingula-flags seem 

 everywhere to underlie the series here as at the other places ; but 

 the Arenig rocks only come in unconformably at the N. E. end of 

 the patch. The beds have very much the same character as at 

 Ramsey Island, with the exception that the middle portion is more 

 of a sandstone in parts, and less cleaved. Some of the most perfect 

 specimens have been found in these last-mentioned beds near and at 

 a place called Paran on the map. 



On the whole, however, Ramsey Island offers the hest advantages 

 for examining these rocks, and also for obtaining fossils, as the beds 

 are there well exposed, and literally, in some parts, almost entirely 

 made up of organic remains. 



The species which have been discovered in these rocks, with the 

 exception of LinguleUa Davisii, are all new, as well as a few of the 

 genera. They comprise a new genus of Trilobites, which I have 

 named Neseurctus, and of which there are several species. This 

 genus forms an interesting stage between the earlier Conocoryphe 



