558 h. kicks on the cambrian and lower silurian rocks. 



Discussion. 



Prof. Ramsay stated that he agreed with much of what Mr. Hicks 

 had said, but doubted whether he was justified in speaking of all 

 the metamorphic rocks referred to as Prae-Cambrian, seeing that in 

 Europe we have metamorphic rocks in all formations, even up to the 

 Eocene. He thought the greater part of the Cambrian and Lower 

 Silurian rocks were deposited in shallow, and perhaps to some 

 extent in fresh water ; the series includes many volcanic rocks of 

 a kind which could not have been thrown up under great sea-depths. 

 Volcanic rocks occur in the Arenig, Llandeilo, and Bala groups, 

 which indeed are chiefly made up of stratified volcanic products. In 

 Cumberland the series consists of volcanic ashes, lavas, &c, with 

 no ordinary sedimentary deposits ; and when the contortions of the 

 strata took place the volcanic ashes were converted into slates. 

 The whole of these were derived from terrestrial volcanoes ; and the 

 same thing had partly happened in Wales. Prof. Ramsay thought 

 it was a great mistake to speak of all these as deep-water deposits. 



Mr. Hicks, in reply, stated that where the rocks which he had 

 mentioned as belonging to the old prse-Cambrian continent were 

 now found exposed they showed every indication of having been 

 old land surfaces before the overlying rocks had been deposited ; 

 and almost invariably the lowest beds in contact with them were 

 either sandstones or conglomerates, whether they belonged to the 

 Cambrian or the Silurian. He even believed that we should find 

 that in Asia Devonian rocks would be found to lie directly on the 

 frontier of this old Laurentian land, which here had remained 

 above the surface during the whole period of the formation of the 

 Cambrian and Silurian rocks in other areas. He believed that land 

 vegetation had gradually attained perfection during these periods 

 on this old Laurentian land, and that air-breathing invertebrates 

 had lived on the areas not reached by water, the progress of develop- 

 ment in marine faunas, land faunas, and land vegetation being for 

 the most part contemporaneous. He believed there was no break in 

 the succession anywhere over the European area until the close of the 

 Lower Silurian ; and he believed that this break only took place in 

 areas which were then subject to volcanic disturbances. Over the 

 larger areas the depression was gradual, and the succession per- 

 fectly continuous from the base of the Cambrian to the commence- 

 ment of the Carboniferous., The sea-bottom during the Tremadoc, 

 Arenig, and Llandeilo periods was at a greater depth than in any 

 previous period ; and though at the close of the Arenig it became 

 much disturbed in some areas by volcanic forces, and covered over 

 by thousands of feet of volcanic matter ejected from submarine vol- 

 canoes, which in some cases heaped up sufficient material to enable 

 them to reach above the surface, yet on the whole it must be 

 considered a period of tolerably deep water ; and the depression must 

 have been continuous to have allowed these great and rapid accu- 

 mulations to be again covered over by conformable sediments. 



