182 THE STORY OF BIRD-LIFE. 



normally sedentary in their habits. Our shores 

 have at different times harboured thousands of 

 the refugees belonging to different orders of 

 birds. 



The most remarkable of these immigrations is 

 that of the Pallas's sand-grouse {Syrrhaptes para- 

 doxus). This bird, an inhabitant of the plains of 

 Tartary, has, so to speak, invaded England on 

 several separate occasions. The first of these 

 was in 1863 when numbers were killed. Another 

 of far greater magnitude occurred in 1888. In 

 Norfolk alone between 10,000 and 12,000 are 

 computed to have been seen, exclusive of the 

 large number killed. 



The cross-bill frequently, and the waxwing 

 more seldom, cross to these islands in more or 

 less numerous bands ; but these occurrences are 

 very irregular, and so far remain entirely unex- 

 plained. 



CHAPTEK X. 



THE DISTRIBUTION OF BIRDS IN TIME AND SPACE. 



The present chapter is intended to serve more 

 or less as a prelude to the one that follows. 



The distribution of birds in time is witnessed 

 by their fossil remains. Thus, if we know the 

 geological formation from which they were taken, 

 we are enabled to gather some notion as to the 

 nature of the bird-life of that particular period 

 of the world's history, and an idea as to the 

 extension backwards in time of this group. 



