Origin of Species Variorum

out; and clear and open oceans may have existed where our continents now stand. Nor should we be justified in assuming that if, for instance, the bed of the Pacific Ocean were now converted into a continent, we should there find sedimentary formations in a recognisable condition older than the Silurian strata, supposing 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 and 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 which formerly 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 appear in our European formations;— the almost entire absence, as at present known, of .. formations rich in fossils beneath the Cambrian 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,