558 THE GEOLOGIST. 
Additional Note on the Geology of Biarritz. — Biarritz is built 
chiefly on a soft sand, passing sometimes into a clay apparently of fresh water 
origin. These bads are very loosely composed and appear to have been much 
distiu'cd by subsidence and slight landslips, they rest unconformably on a sand- 
stone-rock abounding in the numuHtic fossils, also in echini and shells. Going 
south fi-om Biarritz, that is towards the Spanish side, you find the sandstone- 
rock passing into a blue clay. The sand rock overlies the clay ; at their junc- 
tion there is much disturbance, but it is clear that the blue clay underlies the 
sandstone. This is well seen between Yieux Port and the Basque sands. 
From the point where the blue clay cliff begins it is very regular in its struc- 
ture. It continues for at least a mile, dipping uniformly throughout that 
distance to the north-west at an angle of 45 degs. ; the lines of stratification 
are well defined by bands of stone (a sort of clay stone) lighter in colour and 
harder in textiu-e than the mass of the cliff, the clay of which is soft and much 
worn into furrows by the weather, and by the little streams which flow down 
it. Here and there the cliff is capped with beds of sand lying horizon- 
tally on regular strata of yellow, white, and pink colour, much resembling 
the tertiary sands of Alum Bay in the Isle of "Wight. 
At the end of these clay clilis which gradually sink down to the shore, you 
find first recent sand-hills, and a little further beds of sand like those which cap 
the cliff, lying horizontally. Where first they appear low down thus on the 
shore, they are from fifteen to twenty feet high. The uppermost beds are of 
yellow and brownish sand mixed with pebbles ; beneath these is a band of 
orange-coloui'cd clay about three inches thick, very clearly defined, and imme- 
diately below it a dark clay passing downwards into dark brown, and sometimes 
almost black vegetable matter. This, when dry, splits into thin layers like 
card-board, it is full of roots and of stems of fir trees ; I also found impressions 
of seeds ani fir cones, besides masses of leaves of water plants. This bed 
varies from a few inclies to several feet in thickness. Enrther on a dark iron- 
grey sand appeared beneath this bed, but this was only at one pomt. Going 
still south the cliff rises again (after an interval of about half a mile) and 
attains an average height of about forty feet. Here it is composed of tiie hor- 
izontal sands, only with the band of orange clay and the fresh water vegetable 
bed beneath as the base of the cliff. This continues for about a quarter of a 
mile, and then the blue clay of the cliff near Biarritz reappears under tlie 
horizontal sands, dipping as before at a sharp angle, but not so uniformly. At 
one point its beds are thrown up quite edgeways, and tlie numulitic sandstone- 
rock appears intruding beneath it, through the sea-shore sand. The clay 
rests against the sandstone as if the latter had been forced up agaiust it. Here 
there is abundant evidence of great disturbance. 
Not many yards beyond where the sandstone first appears, it appears again so 
different in texture, that it could hardly be recognised as the same rock, were 
it not that it is rich in numulite like the softer rock. In the second instance 
the soft, yellowish sandstone has been changed into a hard, white, and shining 
rock, and where the clay rests against it there is a good deal of crystalization, 
and the clay has been clianged into a rich, pinky brown. All the clay here is 
much more disposed to be shaly than it is near Biarritz, and is harder in con- 
sequence. 
Nearer the water at this point, especially at low tide, are several beds 
quite perpendicular, of which the edges only obtrude ; they appear of a hard 
and beautifully coloured rock, quite Avithout trace of fossils. Near it I ob- 
served some masses of a very dark green amorphous rock ; this is the rock 
called by Mons. Guidres (page 44 of liis little work) Ophite, — Yours, &c., 
A. D. AcwoRTii. 
Eerata in Sir R. I. Murchison's Address to the Geological Sec- 
