36 
tion of strata and mineral deposits. The rule has been 
recalled, that the law, ‘‘ Like causes, like effects,’ does not 
authorise its converse, “ Like effects reveal the same cause.” 
For, as is so obviously clear, two independent causes may 
produce effects exactly similar. Now, much of the supposed 
~ inductive reasoning of treatises on geology is, in reality, but 
an application of this vicious converse. Observation shows 
us a given stratum of rock or indurated sand and slime, re- 
sulting from sedimentary deposition from water. The inference 
is, therefore, all stratified rocks are sedimentary. And some 
treatises on geology assume this unsafe and invalid surmise so 
absolutely as to use the words ‘‘sedimentary” and “‘stratified”’ 
as synonyms. A very plain and useful instance of this sophism 
is given by the case of the Italian savant, who inferred an 
immense age for the strata in a volcanic spot of South Italy, 
by examining a well. The sides of this little excavation 
showed certain strata cf volcanic earth superposed on lava. 
The savant’s assumption was, that all this earth was formed 
gradually by disintegration of hard lava; and as .the process 
is notoriously slow, the thickness of the beds of loose earth 
denoted a vast lapse of time. Now, had he been certain 
that disintegration was the only cause of volcanic earth, his 
inference might have been worth something. But the heed- 
lessness of his logic was put to shame by a very simple 
statement of fact, made by the peasants. Disintegration of 
hard lava was not the only cause of volcanic earth. Another 
cause was dust and ashes, showers from the neighbouring 
volcano. These peasants had been actual eye-witnesses of 
several such emissions, which, guided by a favouring breeze, 
had covered their fields with an inch or two of new soil ina 
single night. And by the simple light of this other cause, 
which the great savant had not thought of, it was clearly 
shown that the accumulation, for which he required many 
scores of centuries, had been the actual work of about two 
hundred years. 
To the candid mind these hints are enough. The most 
careful observer is most fully aware of these facts: that our 
knowledge of the terrestrial energies which have exerted 
themselves in our globe is imperfect; that the grade of speed 
at which known forces are now observed to act, may have 
been exceedingly different at other times and under other 
conditions of temperature and climate; that the causations 
which would need to be accurately determined, in order to 
settle many of these physical questions, were probably com- 
plicated beyond all reach of our observation and ascertainment 
at this late day. 
