DEVONIAN PERIOD 
Pressure -of population, fast increasing, 
With all its strife and rivalry unceasing : 
New forms of life, more vigorous on the stage, 
Climatic changes, epidemics' rage, 
Subsidence, uplift, scarcity of foods, 50 
All bring their trials and vicissitudes ; 
And strained and harried by the wear and tear 
Whole groups of life are doomed to disappear. 
But as, hard pressed, some droop and fade away, 
Others advance and wield a wider sway. 55 
The change around or brings them no distress, 
Or better suits them ; or maybe they possess 
Adaptive powers are able to conform, 
And bending are not broken by the storm. 
Whilst other orders wane and die around, 60 
Along the coasts the " lamp-shells " now abound : 
And pregnant are these creatures with resource 
That bodes long years ere they run out their course. 
Some forms with wing-like shells now meet our eyes, 
Seeming indeed as shelly butterflies. 65 
And though their stock Etruscan-lamp-like be, 
These scarce are " lamp-shells," save by courtesy. 
Nautili are here, whose flattened spiral shells 
Are loosely coiled, and bound with tubercles. 
And though abroad old straight-shelled forms still stray, 70 
These to their coiled allies seem giving way. 
