UPPER EOCENE STRATA OF FRANCE. 
273 
Imperfection of the Record ,—These foot-marks have re¬ 
vealed to us new and unexpected proofs that the air-breath¬ 
ing fauna of the Upper Eocene period in Europe far surpassed 
in the number and variety of its species the largest estimate 
which had previously been formed of it. We may now feel 
sure that the mammalia, reptiles, and birds which have left 
portions of their skeletons as memorials of their existence in 
the solid gypsum constituted but a part of the then living 
creation. Similar inferences may be drawn from the study 
of the whole succession of geological records. In each dis¬ 
trict the monuments of periods embracing thousands, and 
probably in some instances hundreds of thousands of years, 
are totally wanting. Even in the volumes which are extant 
the greater number of the pages are missing in any given 
region, and where they are found they contain but few and 
casual entries of the physical events or living beings of the 
times to which they relate. It may also be remarked that 
the subordinate formations met with in two neighboring 
countries, such as France and England (the minor Tertiary 
groups above enumerated), commonly classed as equivalents 
and referred to corresponding periods, may nevertheless have 
been by no means strictly coincident in date. Though call¬ 
ed contemporaneous, it is probable that they were often sep¬ 
arated by intervals of many thousands of years. We may 
compare them to double stars, which appear single to the 
naked eye because seen from a vast distance in space, and 
which really belong to one and the same stellar system, 
though occupying places in space extremely remote if esti¬ 
mated by our ordinary standard of terrestrial measurements. 
Calcaire siliceux,or Travertin inferieur (A. 2 and 3, p. 252). 
—This compact siliceous limestone extends over a wide area. 
It resembles a precipitate from the waters of mineral springs, 
and is often traversed by small empty sinuous cavities. It 
is, for the most part, devoid of organic remains, but in some 
places contains fresh-water and land species, and never any 
marine fossils. The calcaire siliceux and the calcaire gros- 
sier usually occupy distinct parts of the Paris basin, the one 
attaining its fullest development in those places where the 
other is of slight thickness. They are described by some 
writers as alternating with each other towards the centre 
of the basin, as at Sergy and Osny. 
The gypsum, with its associated marls before described, is 
in greatest force towards the centre of the basin, where the 
calcaire grossier and calcaire siliceux are less fully developed. 
Gres de Beauchamp, or Sables Moyens (A. 4, p. 252).—In 
some parts of the Paris basin, sands and marls, called the 
12 * 
