6 
demanded by the records of the rocks, the ages upon ages required 
for the formation of the stratified rocks, which form so large a 
portion of the crust of the globe, and which contain the records of 
all the past life of which we have any knowledge. But it may be 
fairly doubted whether the theory of uniformity of both action and 
energy, on which the enormous amount of time claimed for past 
geological changes is based, has not been pushed too far ; forces 
similar in kind to those at present in action have, no doubt, had 
their share in time past in the degradation of the older, and con- 
struction of the newer rocks ; but it does not follow either that no 
other forces were in simultaneous operation with them, or that the 
energy with which they themselves acted, may not have been con- 
siderably greater than it is at present. The newly-appointed 
Professor of Geology at Oxford, in his Inaugural Lecture, delivered 
a few weeks ago, answers the question whether all former changes 
of the world’s surface are to be explained by the agency of forces 
alike in kind and degree to those now in action in the negative. 
If the docti'ine of uniformity has been carried too far, we may 
eventually come to regard the first appearance of life upon the 
globe as not so far distant as has sometimes been imagined, and the 
steps of variation in the structure of the fossiliferous strata as not 
having occupied the vast space of time which has been sometimes 
claimed for them. Professor W. C. Williamson, in his lecture on 
Primaeval Vegetation considered with reference to the Origin of 
Species, says, “ that if rve ask an evolutionist what the conditions 
are that he requires for the demonstration of the truth of his 
position, he would tell us at once — unlimited time.” If, then, there 
be any doubt about the time, as Mr. Prestwich seems to indicate 
that there may be, that doubt will weaken the theory of evolution 
at its very root. 
I have said that if species are to be considered unstable, genera 
and families must be considered so also. Are we then to regard 
all the forms of animated nature which we see around us, animal 
and vegetable alike, as mere forms of transition, without any defi- 
nite boundaries, varying indeed in very long cycles, but liable to 
vary in either direction as they may be pressed by external circum- 
