vi PREFACE. 
past history of the earth as revealed by geology, and obtain 
some indications of the existence of those ancient lands which 
now lie buried beneath the ocean, and have left ns nothing but 
these living records of their former existence/’ 
The detailed study of several groups of the birds and insects 
collected by myself in the East, brought prominently before me 
some of the curious problems of Geographical Distribution; 
but I should hardly have ventured to treat the whole subject, 
had it not been for the kind encouragement of Mr. Darwin and 
Professor Newton, who, about six years ago, both suggested that 
I should undertake the task. I accordingly set to work ; but 
soon became discouraged by the great dearth of materials in 
many groups, the absence of general systematic works, and the 
excessive confusion that pervaded the classification. Neither 
was it easy to decide on any satisfactory method of treating 
the subject. During the next two years, however, several im- 
portant catalogues and systematic treatises appeared, which 
induced me to resume my work ; and during the last three years 
it has occupied a large portion of my time. 
After much consideration, and some abortive trials, an outline 
plan of the book was matured ; and as this is, so far as I am 
aware, quite novel, it will be well to give a few of the reasons 
for adopting it. 
Most of the previous writings on Geographical Distribution 
appeared to me to be unsatisfactory, because they drew their 
conclusions from a more or less extensive selection of facts ; and 
did not clearly separate groups of facts of unequal value, or 
those relating to groups of animals of unequal rank. As an 
example of what is meant, I may refer to Mr. Andrew Murray’s 
large and valuable work on the Geographical Distribution of 
Mammalia, in which an immense number of coloured maps are 
