90 SEFSTROM ON THE FURROWS WHICH TRAVERSE 
the surface will not receive a polish and be smooth, a greater | 
friction has been caused against the boulder-stream, and the de-_ 
viation would be greater. 
A third circumstance as regards the determination of the — 
furrows is, that when they are found on a hard mineral which 
receives a fine polish, it would be necessary to stand on such a 
side as to have them quite distinct, so that through the change 
of light and shade they strike the eye. Observations are often 
unsuccessful after dusk; for before one has finished reading off — 
the degrees on the compass, the small furrows have already be- 
come invisible*, 
Nearly everywhere in the southern part of Sweden the moun- 
tains are composed of such compact substances that they readily 
receive the furrows. Such are found here around Fahlun, as 
well as northerly towards Siljan; at Stjernsund; nearly every- 
where in Roslagen ; southerly of Sala; around Arboga ; between 
Link6ping and Atved; around Ronneby; Wimmerby and Eksjé; 
on Tiveden, from Mariestad to Kinnekulle; on Billingen, as 
well as from Lidképing to Wenersborg. It is more certain to 
meet with good furrows on the rocks which have been sheltered 
from the action of the atmosphere, likewise in pits from whence 
material is fetched for repairing the roads, on arable land where 
the rock has been exposed by the plough, as well as on the 
sides of lakes; and above all on the sea-shore, where the rocks, 
from the sinking of the water, or the elevation of the land, have 
been recently exposed. 
It may happen, however, and sometimes on large tracts, for 
example, in the north-western part of East Gothland, as well as 
southerly on the road passing through Westervik, that the 
mountains are composed of such substances as will not receive 
the furrows, or that these in the lapse of time have, through 
* Tt should further be observed in determining the direction of the furrows, 
whether fine and coarse furrows are mixed with each other, also if they run pa- 
rallel, or if they diverge from each other. In the latter case, the direction should 
be determined in the same manner as the finer furrows, because these have, 
without diverging, followed the direction of the flood; but, on the contrary, the 
coarser furrows are traces from the large boulders, which, with their angles and 
more than ordinary force, have rushed against and scrubbed the mountain- 
slope; and as it seldom could occur that this angle ran directly before the 
centre of gravity of this large stone, it may be frequently seen, and in particular 
on coarse-grained substances, that the large furrows go in crooked lines, often 
diverging to the right and often to the left over the fine furrows. On harder 
substances, such as porphyry and trap, they are less crooked. Furrows of this 
kind may be met with on the hard volcanic substances covering the top of 
Billingen, which are of a surprising regularity. 
