AUTHOR’S PRFACE. 
Nearty one third of the present volume appeared a few 
months ago in the form of a series of sketches in the Wit- 
ness newspaper. A portion of the first chapter was submitted 
to the public a year or two earlier, in Chambers’s Edinburgh 
Journal. ‘The rest, amountiag to about two thirds of the 
whole, appears for the first time. 
Every such work has its defects. The faults of the pres- 
ent volume — faults all too obvious, I am afraid — would have 
been probably fewer had the writer enjoyed greater leisure. 
Some of them, however, seem scarce separable from the na- 
ture of the subject: there are others for which, from their 
opposite character, I shall have to apologize in turn to oppo- 
site classes of readers. My facts would, in most instances, 
have lain closer had I written for geologists exclusiveiy, and 
there would have been less reference to familiar phenomena. 
And had I written for only general readers, my descriptions 
of hitherto undescribed organisms, and the deposits of little- 
(ix) 
