71 



which we are so often accustomed under such circum- 

 stances to behold, the results of isolation itself (as an 

 active controlling principle) may be traced out ; whilst 

 geology, ever ready to lend a helping hand when ap- 

 pealed to, will seldom fail to supply those intermediate 

 links of probability which the believer in specific centres 

 of creation must needs subscribe to, before he can draw 

 any deductions on a broad scale, or be competent to 

 analyse even the general bearings of a question fchus 

 necessarily comprehensive. 



Having thought it desirable to defer to a subsequent 

 chapter of this treatise the few geological reflections 

 which our subject may give rise to, it will not be my 

 aim to allude to them in the present section more than 

 is absolutely requisite. I propose rather to consider 

 some of the ordinary effects of isolation, as mere matters 

 of experience ; and to allow geology to tell its own tale 

 when we come to examine the problem of self -dispersion, 

 as occasionally interrupted by subsidence. 



If we except a few of the Heteromera and apterous 

 Curculionida, which appear to be influenced in a dif- 

 ferent manner, the power of isolation over insect form is 

 perhaps more especially to be detected in a deterioration 

 of stature. Whether this principally emanates from the 

 constant irritation of a stormy atmosphere, such as 

 small islands are of course exposed to, and which would 

 seem to have stunted the development (during a long 

 series of ages) of the animal and vegetable worlds, or 

 from a diminution of area consequent on the breaking 



