FOREIGN CORRESPONDENCE. 
205 
What is very remarkable is, that these Tertiary coals are exactly 
like those of the coal-measures proper, whilst the fossil fuel of the 
same age found in Oregon and Washington is non-bituminous. 
It would appear that we have in the coal of Chirigui, formed in the 
Tertiary clays under the tropics, a modern instance of the con- 
ditions in which the coal beds in the coal-measures have been produced, 
thence results the resemblance of .these Tertiary coals with those of 
the coal-measures proper, which, beyond a doubt, were formed under 
a tropical temperature. 
An interesting geological fact is that the coal-measures have 
not yet been traced in South America. All the beds there observed 
belong to the Tertiary epoch. 
On a meam of recognizing the Shores of Ancient Seas. 
M. Marcel de Serres, in a recent letter on a means of 
recognizing the ancient shores of the seas of geological epochs, 
after referring to his studies on the boring-mollusca, points 
out a locality near St. Apolis, in the neighbourhood of Pezenas 
as very interesting. There the cretaceous rocks, which run parallel 
with and adjoin the Mediterranean, are full of thimble-shaped cavities, 
the work of these mollusca. On the north side of the mountain 
nothing of the kind is seen ; the rocks thus perforated are not elevated 
above the level of the soil beyond the point at which they have 
been bored, and the miocene beds rest on them. 
Knowing as we do that the boring-mollusca are to be found in the 
vicinity of the coast-line, are we not justified in looking upon this 
spot as an old sea- shore ? M. Marcel proceeds : — 
" I am now endeavouring, by the consideration of similar facts, 
to determine, by means of the rocks attacked by these animals, the 
localities which mark the extent of the ancient seas, and I believe I 
have succeeded in a locaHty now well known in a geological point of 
view — I mean the basin of Neffier. There the palaeozoic beds are 
boimded on the south-east by the tertiary marine formations ; these 
are composed in certain localities of masses of polyps of the genus 
Astrea, pierced by a great number of Modiolse and Petricolae, and 
others. 
As these different species recede but little from the coast, and the 
polyps occupy the same position as they did in the same sea, they 
seem to represent its ancient margin ; a fact confirmed by their 
position relatively to the Mediterranean, near which these beds are 
situated. 
On the Tertiaries of Bigorre. 
M. Leymerie has communicated to the French Academy a note on 
the Tertiaries of Bigorre, principally studied in the valley of the 
Adour. From this note, which is very interesting, we extract the 
following description of the locality mentioned : — 
