_ A Sketch of the Geology of Texas. 363 
generally an inch or two in diameter, twisted both Ways, and 
mostly fturowed longitudinally on the surface. At first view I 
was rather puzzled as to their relations, but on closer inspection 
of their internal structure, it became evident that they must be- 
long to the order of the Hippurites, that singular division of shells 
which gives the peculiar fossil character to the. cretaceous forma= 
tion of Southern Europe, from Lisbon in Portugal as far as Asia 
Minor along the Mediterranean. Some beautiful specimens of a 
real: Hippurites resembling very much a species of Southern 
France, were afterwards met: with. In the same beds of lime- - 
Stone with these Hippurites, several species of bivalve shells are 
found which belong to genera equally characteristic of the Medi- 
terranean cretaceous formations, viz. Diceras and some analogous 
Senera. At last in the same beds also occur a large Pecten of the 
same section as the Pecten quadricostatus, besides several univalves. 
_ Some Hippurites and several species of the Diceras family, 
Were also found on the Piedernales; so that it seems probable 
_ that the strata just described have a very extensive range. 
“ Having presented the facts observed, I offer a few general con- 
clusions from them. At first there cannot be the least doubt that 
all the strata just described are equivalent to the cret forma- 
tion of Europe. ‘The identity in the general character of the fos- 
Sils ineontestibly proves it.» It is more doubtful to which division 
Of the cretaceous formation they ought to be referred. So much 
however is certain a priori, that they do not represent the lowest 
divisions of the cretaceous system; since among the organic re- 
Mains there are no characteristic fossils of the lower green sand 
orof the gault. 'The fossils of the white marly limestone first 
Mentioned indicate an age not older than that of the “chalk 
marl” of England in the series of the cretaceous deposits of 
Europe. We might even be inclined to believe those strata equiv- 
alent to the white chalk of Europe, if some of the most charac- 
teristic fossils of the chalk among them especially the Belemnites 
mucronatus were not wanting altogether. The system of strata 
Partly consisting of compact siliceous limestone, and contain 
fossils of the Hippurite order, next described, belong still high- 
er in the*European series; for near New Braunfels they cer- 
tainly lie above the marly limestone. From some observations 
| ver made at other localities, 1 have reason to believe that 
the two systems of strata are not every where so distinctly sepa- 
