426 
THE GEOLOGIST. 
of the manner in which God has chosen to deal with His material 
universe." 
The author then adopts, as the fundamental principle of geological 
reasoning, that — " The 2)h''nom.ena which geology presents to us as 
objects of x>hysical investigation cere to he referred to natural causes, so 
far as it can be shoion that they tvould be the necessary consequences of 
each causes acting under conditions, the former existence of which may 
he deemed admissible. 
" The limitation expressed in the preceding enunciation is ohvioxisly 
necessary, in drawing the line of demarcation between those conclusions 
of the science which rest on certain, and those which rest on contro- 
vertible principles. Some assumption must also be made as to the nature 
and action of the natural causes of which we recognize the agency in 
those remote ages to which geology refers." If researches analogous to 
those which have been crowned with such complete success in reference 
to the solar tystem should hereafter be made with respect to thoso 
nebuloD or clusters of stars which lie in the remoter regions of space, 
they will doubtless be founded on the hypothesis of the universality of 
gravitation, and of the laws which regulate the production and propa- 
gation of light, heat, and electricity, or of any other physical law which 
may be necessary in our investigations. And the same invariability 
which we are prepared to recognize in reference to space, we would 
equally recognize in reference to time ; and would distinctly assert the 
law, that cdl physical causes acting under given conditions are to be 
regarded as having 2')Toduced, in cdl j^ast time, the same effects as the 
same causes, acting under the same conditions, would produce at the 
present time. Thus we assume the constancy of the law according to 
which different particles of matter attract each other, and also of the 
laws which govern the propagation of heat through solid and fluid 
bodies, and of its influence in converting solids into fluids, or fluids 
into gases. In short, we assume that all physical causes have always 
acted according to the same laws, and, when acting under identical 
conditions, with the same intensity. 
Tqis hypothesis has been more or less confounded with another 
hypothesis — that the earth must have been for an indefinite period 
of time in a physical state essentially the same as that in which it now 
exists. To confound them is a great error ; for it is extremely difii- 
cult to understand how the causes of which we recognize the agency 
in geology can have continued to operate for an indefinite length of 
time without changing the state and condition of the terrestrial mass 
on which tbey have been acting. 
As some curves, known to geometricians, are so nearly related to 
straight lines, that, if we were to examine any part of the extended 
portion running besides its asymptote, it would appear so like the straight 
line that our senses would not appreciate the difference, " so it may 
be with our planet. However slow may have been the process of 
change, even during all geological time, it may have been like the tardy 
change of direction in our curve in its infinitely extended branch, 
towards its asymptotic direction. It may be that the earth, instead of 
having never deviated materially from its present physical condition, 
