XXXU PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



slates of Sweden), an Olenus, and Conocephalus occur along with the 

 characteristic Lingulce of the deposit ; and an upper, where the same 

 genera are accompanied by a few Brachiopoda and Bryozoa, as in 

 Bohemia. But whereas in the latter country no passage can be shown 

 of this fauna into the Silurian stage above, in Wales a palseontological 

 passage from the Lingula beds into the Bala or LlandeUo group 

 appears to be indicated. This is marked by the association in the 

 upper part of the igneous series of two large species of Olenus with 

 Agnostus and Lingulce, and with types unquestionably characteristic 

 of the Llandeilo beds, such as Asaphus, Calymene, and Ogygia, and 

 Graptolites of species undistinguishable from those of the Llandeilo 

 flags. 



The interesting memoir of Dale Owen leaves no doubt upon the 

 equivalence to these beds of the Potsdam sandstone of North America, 

 in which Trilobites of the Paradoxides type are mingled with the 

 Lingulse, so characteristic of this formation. 



The demonstration of this important zone of life, the earliest as yet 

 distinctly traced, is a great step in Palseozoic Geology, one firmly 

 established during the past year. 



The extinction of the primordial fauna in Bohemia is attributed by 

 M. Barrande to the eflFects of the igneous eruptions manifested by 

 the masses of porphyries interposed between his lowest fossiliferous 

 and the succeeding stage. The destroying mfluence of trappean 

 eruptions are more than once laid stress upon by him. Similar phse- 

 nomena appear to have terminated the Lingula-flag epoch in the 

 Welsh area ; volcanic outbursts, as remarked by Professor Ramsay, 

 " in consequence of which great ashy deposits were found interstra- 

 tified with ordinary muddy sediment, and here and there associated 

 with thick beds of felspathic lava." But these outbursts do not 

 always appear to have had so decided an influence upon the faunas 

 of ancient seas, for, in the instance of Wales, the great eruptions that 

 occurred during the epoch of the deposition of the succeeding Bala 

 beds did not materially affect the population of the oceanic area in 

 which they broke out. For my part I am strongly mclined to think 

 that the influence of volcanic outbursts upon life through the de- 

 structive agency of the products of eruptions has often been over- 

 rated. Igneous overflows, showers of ashes, and exhalations of 

 deleterious vapours are necessarily destructive, but as necessarily 

 local, and scarcely hkely, arguing at least from all cases of which we 

 have sufiicient knowledge, to extinguish the fauna and flora of a 

 whole natural-history province, much less of many provinces. But 

 they are the certain indications of far more powerful though less con- 

 spicuous and less traceable enemies of life. They are often the 

 indices of epochs of excessive disturbances of the earth's crust, and 

 of elevations and depressions of the surface of the sea-bed. Changes 

 of level and consequent changes of surrounding conditions, even to 

 the extent of change of medium, are the great life-extinguishers. 

 The degree of substitution in an ancient fauna should rather be 

 accepted as an evidence of the extent of the moTcments that have 

 taken place during an age of Tolcanic energy, than as a measure of 



