IN EVOLUTION FROM A GEOLOGICAL POINT OF VIEW. 175 
bounds :—for instance, Lingula of the Recent compares with 
Lingulella of the Cambrian, Rhynchonella of the Recent with 
Rhynchonella of the Ordovician, Heliopora of the Recent with 
Heliolites of the Ordovician, Nautilus of the Recent with 
Nautilus of the Silurian.* Thus some animals have traversed 
almost the whole of known fossiliferous time with barely 
generic variation. Hence, returning to our diagram, we 
have to draw to the circumference of the Recent Period 
these radii almost parallel throughout the known life-ages 
before producing them backwards to find the centre of 
original protoplasm. It may be questioned indeed whether 
there is in them any divergence at all; whether for imstance 
Heliopora is more differentiated than Heliolites; but even 
granting this, it is, on the basis of extreme evolution, pure 
assumption to assert, that in the pre-fossiliferous ages they 
had diverged more rapidly than they afterwards did in the - 
fossiliferous ages. No sufficient reason for such a cessation 
of advance has been given; if anything it would be more 
reasonable to suppose that the poteucy of evolution increased 
rather than diminished with the progress of time and the 
advance of organic grade. But this is to make the pre- 
fossiliferous ages hugely vaster than the fossiliferous ages. 
Yet already we know how difficult it is becoming, even on a 
very much modified uniformitarian basis, to account for the 
accumulation of sediment shown by the fossiliferous ages in 
the time (the lessening time) allowed by physicists for the age 
* (Ehlert in Fischer’s Manuel de Conch., 1887, placing it as a sub- 
genus of Lingula, remarks, “it is the most ancient form of Brachiopod 
actually known.” 
