XV.] CAMBRIAN AND SILURIAN IN EUROPE. 375 



distance of eleven miles to the northwest, however, the Tre- 

 inadoc slates disappear, and the Lingula flags are represented 

 by only 2,000 feet of strata ; while in parts of Caernarvonshire, 

 and in Anglesea, the whole of the Lingula flags and, moreover, 

 the Lower Cambrian rocks are wanting, and the Llandeilo beds 

 rest directly upon the ancient crystalline schists. In Scotland 

 and in Ireland, moreover, the Lingula flags are wholly absent, 

 and the Llandeilo rocks there repose unconformably upon 

 grits regarded as of Lower Cambrian' age. Thus, without 

 counting the Tremadoc slates, which are a local formation, 

 unknown out of Merionethshire,* we have (including the 

 Bangor group and Lingula flags), beneath the Llandeilo, over 

 9,000 feet of fossiliferous strata, which disappear entirely in 

 the distance of a few miles. From a careful survey of all the 

 facts, the conclusion of Ramsay is irresistible, that there exists 

 between the Lingula flags and the Llandeilo not merely one, 

 but two great stratigraphical breaks in the succession ; the one 

 between the Lingula flags and the Lower Tremadoc slates, and 

 the other between the Upper Tremadoc slates and the Lower 

 Llandeilo, at the base of which were included the Arenig rocks. 

 This conclusion is confirmed by the fact that there exists at 

 each of these horizons a nearly complete palaeontological break. 



* [This statement requires correction, since already, in 1866, Messrs. Salter 

 and Hicks had mentioned the occurrence of rocks supposed to be of that age 

 near St. David's in South Wales, and very recently, in the Quarterly Geologi- 

 cal Journal for February, 1873, the latter has given a description of the 

 localities of Tremadoc rocks in this region, with figures of the organic remains, a 

 map, and sections. The beds have here a thickness of about 1,000 feet, and rest 

 directly upon the Lingula flags. The apparent want of conformity between the 

 two divisions noticed by Ramsay in North Wales is here not manifest. They 

 are followed in seeming unconformity by the Arenig rocks, which are by Mr. 

 Homfray considered equivalent to the Upper Tremadoc of North Wales, and 

 contain in abundance the graptolites of the Levis formation of Canada. The 

 beds between these and the Lingula flags hold a rich fauna closely allied to 

 the Lower Tremadoc, including an Orthoceras, a new species of Paleasterina, 

 and a Dendrocrinus, various brachiopods and lamellibranchs, trilobites of 

 the genus Niobe and of a new genus, Neseuretu^, closely allied to Dikeloceph- 

 alus, to which Hicks refers the supposed species of D. described by Salter 

 from the Upper Lingula and Lower Tremadoc rocks of North Wales ; the only 

 true Dikelocephalus in Wales, according to him, being D. furca from the 

 Upper Tremadoc.] 



