146 NATURAL SCIENCE [September 
of the interesting problems connected with the history of the Arctic 
regions. In the first paper, a summary is given of the geological 
structure of the land masses surrounding the Arctic Ocean; the 
variations in the relative positions of land and water are traced, and 
it is argued that the Polar Basin has been formed by subsidence 
during Tertiary times. In the second paper, the author considers 
the changes in climate that have taken place in the North Polar 
Regions. He refers to the famous theory according to which the 
Arctic regions were once clothed in tropical vegetation and their 
shores were once fringed by coral reefs. The evidence on which 
this theory rests is, however, shown to be very untrustworthy. The 
plant determinations made by Heer are unreliable, and there is no 
evidence that coral reefs were ever formed within the Arctic Circle. 
Corals grew in Arctic seas in earlier times as they do to-day, but 
there has been no adequate proof that they ever formed reefs. Dr 
Gregory accordingly distrusts all the theories as to the great size of 
the sun in Palaeozoic times and the universal uniform climate in 
the pre-Tertiary period, which have been based on the asserted 
Arctic palm-groves and coral seas. That climatic changes have 
occurred is not disputed, but the author does not think it possible 
to estimate their extent until the palaeontology of the Arctic regions 
has been carefully revised. The most important work on this 
subject now being carried on is Professor Nathorst’s redescription of 
the fossils about which Heer theorised so wildly. Dr Gregory also 
concludes that palaeontological evidence tells strongly against the 
view that the position of the Poles has altered to any great 
extent. 
BIRDS AND THEIR STOMACHS 
THE United States Department of Agriculture, knowing that the 
welfare of the country depends largely on the prosperity of the 
farming class, has undertaken for long past a proper consideration 
of birds in their relation to agriculture. In its fifty-fourth bulletin 
it deals with the stomach-contents of some twenty common birds. 
Among these may be mentioned the cuckoos, woodpeckers, bluejays, 
ricebirds, blackbirds, orioles, cedarbirds, catbirds, bluebirds, &c. 
There is a good deal of practical common-sense in the introduction 
of this pamphlet by Mr F. E. L. Beal, who points out the tendency 
to dwell on the harm done by birds rather than the good. He goes 
on to say :— 
“ Within certain limits, birds feed upon the kind of food that is 
most accessible. Thus, as a rule, insectivorous birds eat the insects 
that are most easily obtained, provided they do not have some 
peculiarly disagreeable property. It is not probable that a bird. 
