110 SEFSTROM ON THE FURROWS WHICH TRAVERSE 
vour to form an idea of the occurrences which have passed ; and 
this conjecture, which in other sciences would be an unwar- 
rantable assumption, instead of the result of a well-grounded in- — 
vestigation, is in geology a necessary and essential part of the 
science. In the mean time conjectures are made in various 
ways, according to the different views taken by different persons ; 
and the opinions of those who have made the nearest approach 
to the geological cause, have never the confirmation of cer- 
tainty. I therefore foresee that the phenomenon which I have 
described may possibly by many be ascribed to other causes than 
those which according to my own views appear most probable 
for explaining the origin of the furrows and boulders. 
§ 5. 
Of the period when the Boulder-flood took place. 
If we trace the furrows on a hard rocky substance which is 
not acted upon by the atmosphere, we might believe that they 
were formed only a few years back, and that they never could 
be a monument of events more ancient than the commencement 
of human chronology. Should we assume, with some geologists, 
that the action of the atmosphere on the mountains has formed 
the valleys, this would oblige us to infer that the boulder-fur- 
rows in various places were not many centuries old. But that 
such a notion must evidently be incorrect, is to be inferred 
from two certain facts. The first is that which has come to our 
knowledge through the investigations made during Napoleon’s 
Egyptian campaigns, that in the blocks of stone found remaining 
at the quarries from which the building materials were taken for 
the pyramids, and which appearing to have been too large for 
them to remove, were thus left in their rough-hewed state, the 
marks of the chisel remain as fresh as if they had been made 
only a few years back; they are, however, now nearly three 
thousand years old*. Secondly: At the great fall of Avesta, 
as well as at the so-called little fall, various slabs are to be 
found with uncommonly beautiful furrows, which make an angle 
of from 75° to 86° towards the present direction of the Da- 
lelfven. The Dalelfven has also passed over these furrows 
perhaps at a much remoter epoch than when the Egyptian 
* The pyramids themselves are said to be covered with limestone slabs which 
are decomposed by the atmosphere. 
