JuLY 2, 1897.] 
Speaking of the Rhine, mention may be 
made of a geological essay by Rothpletz, of 
Munich ( Das Rheinthal unterhalb Bingen, 
Jahrb. k. preuss. geol. Landesanst., 1896, 
10-39 ), in which it is shown that for about 
four kil. in the head of the gorge it follows 
close upon a narrow block between two 
sub-parallel faults of considerable disloca- 
tion. Although no vertical movement is 
proved for the block, the author concludes 
that there was a ‘direct genetic connection’ 
between the dislocation and the origin of 
the gorge, for similar disturbances seem to 
be wanting in the uplands (Taunus) further 
east. It may, however, be objected that 
until the date of the dislocation is shown to 
be recent, and until the movement of the 
block is shown to be downward, it is pre- 
mature to make too close an association of 
these two phenomena. If, as is very possi- 
ble, the dislocation is ancient, all sorts of 
happenings may have intervened before the 
river gained its present course; and among 
the factors that determined its location, the 
dislocation may have had a relatively sub- 
ordinate rank. ‘To place ancient structural 
disturbances in direct genetic connection 
with the location of a very modern river 
gorge suggests that a great many interme- 
diate processes are overlooked. 
THE GEOGRAPHY OF BRITTANY. 
PROFESSOR CHARLES BARRO!IS, of Lille, long 
occupied on the intricate geology of Brittany, 
has recently presented a summary of its 
geographical divisions, with a special chap- 
ter on the influence of its physiography on 
its advance in civilization (Ann. de Geogr., 
VI., 1897, 23-64, map). The region is com- 
posed of ancient rocks, strongly folded and 
dislocated on east and west lines, whose 
trend diverges inland. To-day the surface 
is that of a dissected peneplain, with even 
skylines and a gradual descent to the 
north and south, the former steeper than 
the latter. The author believes that the 
SCIENCE. 
23 
ancient mountains indicated by the struc- 
ture have been removed by subaérial weath- 
ering and washing, not by marine erosion. 
The existing longitudinal drainage lines do 
not occupy synclinal axes, but follow open 
valleys or combes along the strike of weak 
strata, after the fashion of subsequent 
streams. The transverse rivers, by which 
the inner belts of low ground are drained, 
cross the uplands in sharp trenches or 
cluses, across which viaducts and suspension 
bridges are carried above the steeples of the 
valley villages. These transverse streams are 
called consequent, as if determined by the 
lateral slopes of the original deformation 
(post-Carboniferous); their possible origin 
by superposition from a Mesozoic cover, 
now stripped away, is not explicitly con- 
sidered. In this respect the suggested com- 
parison of the drainage on the ancient folded 
structure of Brittany with the rivers of the 
relatively young and simple dome of the 
English Weald does not seem to be fully 
warranted. 
INSEQUENT RIVERS. 
Init1Au land forms, due to uplift, defor- 
mation and other non-destructive processes, 
are gradually carried through a systematic 
series of sequential changes, chiefly under 
the action of streams, sometimes under the 
action of waves, wind or ice. Omitting 
antecedent streams from present considera- 
tion, the first streams to be developed on an 
initial surface are the consequent streams, 
so named by Powell. If the valley sides 
of the consequent streams lay bare a dis- 
ordered structure of variable resistance, gul- 
lies and ravines will grow along the guidance 
of the weaker structures, and thus subse- 
quent streams will be developed by head- 
ward erosion; the term subsequent being 
first used in this connection by Jukes, al- 
though not in a technical sense. It some- 
times happens that no guiding weak 
structures are revealed on the consequent 
