4 
cession theory of Lieut. -Col. Drayson, who refers it to a great 
increase in the obliquity ; and, fourthly, the view advocated 
with great labour and ability by Mr. Croll, in his work 
“ Climate and Time.” He there employs more than 500 pages 
in attempting to prove that a series of glacial periods have 
been due to successive maxima of excentricity of the earth's 
orbit during a space of three millions of past years. 
II. — The Doctrine of Uniformity. 
4. The title of Sir C. Lyell's work is “ Principles of 
Geology ; or an Attempt to Explain the Former Changes of 
the Earth's Surface by Reference to Causes now in Operation.'' 
And he recommends an “ earnest and patient endeavour to 
reconcile the former indications of change with these existing 
causes.'' And in Mr. Page's Advanced Text-book we are 
told, “ When such hypotheses as nebular condensation, 
igneous fluidity, change of axis, secular contraction of the 
earth's mass, highly carbonated atmosphere, passage of the 
system through colder and warmer regions of space, are 
advanced to account for geological phenomena, the student 
must receive them as mere hypotheses, not as the true and 
sufficient causes of inductive philosophy. The legitimate 
progress of science lies over a pathway of observation, fact, 
and deduction, and is little aided by conjecture, however 
plausible. Let us strive first to exhaust the range of normal 
causation in existing nature, and even then continue to work 
and watch, rather than fall back on the idle and unphiloso- 
phical resort of abnormal conditions in primeval nature.'' 
And, again, p. 374, “ There are two great schools of geology, 
the one ascribing every result to the ordinary operations of 
nature, combined with the element of unlimited time ; the 
other, appealing to agents that operated during the earlier 
epochs of the world with greater intensity, and over wider 
areas. The former belief is certainly more in accordance 
with the spirit of right philosophy, though it must bo 
confessed that many problems in geology seem to find 
their solution only through the admission of the latter 
hypothesis.'' And Sir C. Lyell, in his “ Treatise on the 
Antiquity of Man,'' though his statements are indefinite, 
says, that the historical period seems “ quite insignificant 
in duration, when compared with the antiquity of tho human 
race'' (p. 289), “and that natural barriers would ensuro tho 
isolation, for tens of thousands of centuries, of tribes in a 
primitive state of barbarism'' (p. 380). This implies a con- 
