302 THE CANADIAN NATURALIST. [Vol. vi. 



Sweden, who places the line between Cambrian and Silurian 

 at the base of the Llandeilo or the second fauna. It was by 

 following these authorities that I, inadvertently, in my address 

 to the Amsrican Association for tlie Advancement of Science in 

 August, 1871, gave this horizon as the original division between 

 Cambrian and Silurian. The reader of the first part of this 

 paper will see with how much justice Sedgwick claims for the 

 Cambrian the whole of the fossiliferous rocks of Wales beneath 

 the base of the May Hill sandstone, including both the first and 

 the second fauna. I cannot but agree with the late Henry Darwin 

 Rogers, who, in 1856, reserved the designation of " the true Euro- 

 pean Silurian " for the rocks above this horizon. [Keith Johnson's 

 Physical Atlas, 2nd ed.] 



The Lingul i-fl igs and Trcmadoc slates have been made the 

 subject of careful stratigraphical and paleontological studies by 

 the Geologic il Survey, the results of which are set forth by 

 E- imsay and Salter in the third volume of the Memoirs of the 

 Geological Survey, published in 1866, and also, more concisely, in 

 the Anniversary Address by the former to the Geological Society 

 in 1863. [Geol. Jour. XIX, xviii.] The Lingula flags (with 

 the underlying Menevian, which resembles them lithologically) 

 rest in apparent conformity upon the purple Harlech rocks both 

 in Pembrokeshire and in Merionethshire, where the latter appear 

 on the great Merioneth anticlinal, long since pointed out by Sedg- 

 wick. The Lingula-fl igs, (including the Menevian) have in this 

 region, according to Ramsay, a thickness of about 6000 feet. 

 Above these, near Tremadoc and Festiniog, lie the Tremadoc 

 slates, which are hero overlaid, in apparent conformity, by the 

 Lower Llandeilo beds. At a distance of eleven miles to the 

 north-west, however, the Tremadoc slates disappear, and the 

 Lingula-flags are represented by only 2,000 feet of strata 5 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 (includ- 

 ing the Bangor group and Lingula-flags,) beneath the Llandeilo, 

 over 9,0U0feet of fossiliferous strata, which disappear entirely in 



