Origin of Species Variorum

such to have been formerly deposited; for it might well happen that strata which had subsided some miles nearer to the centre of the earth, and which had been pressed on by an enormous weight of superincumbent water, might have undergone far more metamorphic action than strata which have always remained nearer to the surface. The immense areas in some parts of the world, for instance in South America, of naked metamorphic rocks, which must have been heated under great pressure, have always seemed to me to require some special explanation; and we may perhaps believe that we see in these large areas, the many formations long anterior to the Silurian epoch in a completely metamorphosed but likewise denuded condition.

The several difficulties here discussed, namely— that, though we find in our geological formations many links between the .. species which now exist and have existed, we do not find infinitely numerous fine transitional forms closely joining them all together;— the sudden manner in which several whole groups of species first appeared in our European formations;— the almost entire absence, as at present known, of .. formations rich in fossils beneath the Silurian strata,— are all undoubtedly of the most serious nature. We see this in the ... fact that .. the most eminent palæontologists, namely Cuvier, .. Agassiz, Barrande, Pictet, Falconer, E. Forbes , &c., and all our greatest geologists, as Lyell, Murchison, Sedgwick, &c., have unanimously, often vehemently, maintained the immutability of species. But it is evident from the recent works of Sir Charles Lyell that he now almost gives up this view; and some other great geologists and palæontologists are much shaken in their confidence. I feel how rash it is to differ from the foregoing