I9I3.] STEVENSON— FORMATION OF COAL BEDS. 119 



strong elective affinity for facts of one type in preference to those of 

 another. At the same time, when one finds that the hypotheses are 

 wholly antagonistic, he is compelled to believe that some must be 

 wrong, and he is led to suspect that the best may be defective. 



In considering the several hypotheses, the writer will take for 

 granted that, as the laws of physics are unchangeable, physical agents 

 have always acted in the same way as now, though at times their 

 activity may have been greater and more prolonged than at others ; 

 That a hypothesis, to be acceptable, must not be based on assump- 

 tions, which are themselves hypothetical or not conceivable in terms 

 of conditions actually known to exist ; That inasmuch as knowledge 

 is still imperfect, no hypothesis, satisfactory in all details, can be 

 framed and that there must remain many matters to be studied by 

 investigators in the future. There is no assertion of uniformitari- 

 anism beyond that of physical law. 



Defenders of the several hypotheses should meet on equal terms 

 in respect to introduction of evidence. Advocates of one group of 

 hypotheses must not arrogate to themselves the right to utilize one 

 type of evidence while denying that right to their opponents. It is 

 hardly legitimate to denounce as tyranny the doctrine of Modern 

 Causes, on one page, while on a later page of the same memoir, a 

 luckless adversary is swept from the arena by the contemptuous 

 assertion, that nothing of the kind is known in recent times. It must 

 be remembered that, in this study, both inductive and deductive rea- 

 soning are required. No man ever explored the Carboniferous 

 forests, mapped Carboniferous topography or sailed a Carboniferous 

 sea. Those who defend the doctrine of Ancient Causes, equally with 

 those who defend the doctrine of Modern Causes, reason from the 

 known present to the unknown past. The starting point is absolutely 

 the same for all. Evidence of every kind must be welcomed and 

 an effort made to determine its value. Stratigraphers may not reject 

 the testimony of palaeontologists nor may the palaeontologists speak 

 slightingly of the stratigraphers. For either group to dwell lovingly 

 on errors of the other, committed many years ago, is as absurd as is 

 the effort to discredit the work of modern Egyptologists because 

 their predecessors of half a century ago, in their anxiety to reconcile 



