由于现存的各式生物都是远在志留纪前就已存在的生物的直系后代，我们可以肯定代代相接的通常延续过程从未中断过，也从未有过大灾变使整个世界遭受破坏。

• As all the living forms of life are the lineal descendants of those which lived long before the Cambrian epoch, we may feel certain that the ordinary succession by generation has never once been broken, and that no cataclysm has desolated the whole world.