Ch. XXIII.] SUPPOSED UNIVERSALITY OF RED MARL. 333 
stratum, and even if these abound and are specifically different 
from the fossils of the supposed European equivalent, it may- 
be objected, that we cannot expect the same species to have 
inhabited very distant quarters of the globe at the same time. 
Supposed universality of red marl. — We shall select a remark- 
able example of the erroneous mode of generalizing now alluded 
to. A group of red marl and sandstone, sometimes containing 
salt and gypsum, is found in England interposed between the 
lias and the carboniferous strata. For this reason, other red 
marls and sandstones, associated some of them with salt and 
others with gypsum, and occurring not only in different parts 
of Europe, but in Peru, India, the salt deserts of Asia, those 
of Africa, in a word, in every quarter of the globe, have been 
referred to one and the same period. The burden of proof is 
not supposed to rest with those who insist on the identity of 
age of all these groups, so that it is in vain to urge as an ob- 
jection, the improbability of the hypothesis which would imply 
that all the moving waters on the globe were once simulta- 
neously charged with sediment of a red colour. 
But the absurdity of pretending to identify, in age, all the 
red sandstones and marls in question, has at length been suf- 
ficiently exposed, by the discovery that, even in Europe, they 
belong decidedly to many different epochs. We have already 
ascertained, that the red sandstone and red marl with which 
the rock-salt of Cardona is associated, may be referred to the 
period of our chalk and green-sand *. We have pointed out 
that in Auvergne there are red marls and variegated sand- 
stones, which are undistinguishable in mineral composition, 
from the new red sandstone of English geologists, but which 
were deposited in the Eocene period ; and, lastly, the gypseous 
red marl of Aix in Provence, formerly supposed to be a marine 
secondary group, is now acknowledged to be a tertiary fresh- 
water formation. 
* I was led to this opinion when I visited Cardona in 1830, and before I was 
aware that M. Dufrenoy had arrived at the same conclusions, Ann. des Sci. Nat., 
Avril, 1831, p. 449. 
I 
