558 Geological Society of Glasgow. 



so many contradictions, and is after all so utterly barren, that we 

 are comj)elled to seek for some theory which shall show that the 

 classification of animals depends on the right understanding of laws 

 continuously operative throughout all time. Descent, with modifi- 

 cation, is the probable origin of our present faunas, but that descent 

 must be compatible with the continuance, unaltered for a shorter or 

 longer period, of some at least of the plans of structure ; must have 

 been so far under external influences that the causes of change have 

 been at all times variable in amount and in extent of action ; other- 

 wise, at present, we should see around us only the higher forms, the 

 lower having succumbed to a universal law of change. The spirit 

 of this view is contained in a pregnant sentence by one of our 

 highest authorities in Botany, who has contributed much by his 

 writings to the philosophic cultivation of Natural History. Dr. 

 Hooker, in his Mora of Tasmania, says " The degree or amount of 

 variation may be assumed as differently manifested at different 

 epochs in the history of the group," and goes on, " as all the highest 

 orders of plants contain numerous species, and even genera, of as 

 simple construction as any of the lower orders are, it follows that 

 the physical superiority which is manifested in greater extent of 

 variation, in better securing a succession of race, in more rapid multi- 

 plication of individuals, and even in increase of bulk, is in some 

 cases of a higher order than that represented by mere complexity or 

 specialization of organ." 



2. An ordinary meeting of this Society was held on November 7th, 

 Professor Young, M.D,, F.R.S.E., President, in the chair. The 

 following papers were then read : — 



I. On the Order of Succession among the Silurian Eocks of Scot- 

 land. By Archd. Geikie, Esq., F.E.S., Director of the Geological 

 Survey of Scotland. The Silurian rocks may be regarded as the 

 framework of the country. They spread over the Southern uplands, 

 and then, sinking under the central valley of the Lowlands, rise up 

 on the farther side in a metamorphosed form, and stretch far and 

 wide as the gneisses, schists, limestones, and quartz rocks of the 

 Highlands. It is, of course, in the unmetamorphosed or southern 

 belt that the order of succession among the Scottish Silurian rocks 

 must first be studied. The contortions in this southern belt obscure 

 the relations of the beds ; but viewed on the great scale, a longitudi- 

 nal axis is seen to traverse the chain in a N.E. and S.W. direction, 

 crossing Annan valley, a little south of Beattock. This central 

 portion must therefore be of older date than those towards the mar- 

 gins where Upper Silurians are found on the north at Lesmahagow 

 and the Pentlands, on the south in Kirkcudbright. Pending the 

 detailed mapping of the country, the succession seems at present to 

 range from Llandeilo Flags, represented by the beds along the axis, 

 to the Lower Llandovery, to which certain Ayrshire beds seem to 

 belong. The hard grey grits, greywacke sometimes conglomeratic 

 or brecciated, blue, red, or olive shales, and occasional but inconstant 

 bands of limestone, which make up nearly the whole of the Southern 



