38 GEOLOGICAL MEMOIRS- 



n tlie districts containing limestone rocks, whilst it is rare to find 

 them in other formations where the running water ajjpears'to be^in- 

 capable of furnishing these crustaceans with an amount of calcareous 

 matter sufficient for the formation of their integimient. Analogous 

 considerations may perhaps contribute to explain the absence or rarity 

 of testaceous animals in certain geological formations. [J. N.] 



On a new Pyreneari Type parallel to the Chalk. By M. Leymerie. 



[Coraptes Rendus, torn, xxviii. p. 738-740.] 



This formation has been particularly studied near Monleon and 

 Gensac, between the Hautes-Pyrenees and Haute-Garonne, where the 

 fossils are abundant and easily collected, but extends over the whole 

 breadth of the latter department. In these localities it usually occu- 

 pies the sides of hills, the summits of which consist of the tertiary 

 formations. It is composed of j^ellowdsh and grey marls and marly 

 limestones, resting on a white limestone with very few fossils, and is 

 of moderate thickness. The strata, badly characterized, in general 

 dip irregularly towards the north. In regard to its geological position, 

 it is placed between two systems ; the lower composed of limestones 

 and tjlack slates, with conical orbitolites and caprotinse {calcaire a 

 Dicer at es^ Dufrenoy) ; the upper the terrain a mimmulites or ejpi- 

 cretace. 



Its fossils have been carefully studied. In forty-two well-marked 

 species, twenty-five are new ; the remaining seventeen belong to almost 

 all the chalk-beds from the craie chloritee to the upper Maestricht 

 chalk. The chief species of the lower chalk are, Ostrea lateralis^ 

 Nilsson ; Terehratula alata, Lamk.; Ammonites Leivesiensis, Sow. ; 

 Baculites anceps, Lamk. Those indicating the common white chalk 

 are, Aiianchytes ovatus{y2ir.), Lamk.; Pecten striatocostatus,Go\M. ; 

 Spondylus Dutempleanns, d'Orb. ; Ostreav esicidaris, Lamk. ; O. 

 Larva, Lamk. ; Terehratula alata, Lamk. Lastly, a very marked 

 analogy with the chalk of JVIaestricht is indicated by the following 

 fossils : — Hemipneustes radiatus, Agass. ; Thecidea radiata, Def. ; 

 Natica rvgosa, Han. ; Pecten striatocostatus, Ostrea vesicularis and 

 O. Larva. These fossils are not disposed in groups according to their 

 supposed antiquity, but occur mixed together at all vertical heights. 

 The ammonites and baculites, indeed, are found only in the lower 

 beds, but along with fossils of the white and even of the Maestricht 

 chalk. 



A remarkable palseontological paradox is the presence, as common 

 and characteristic fossils in the lower part of the marly system, of the 

 Terehratula Venei, Leym. and the Ostrea lateralis, Nils., species 

 which occupy a no less important place in the department of the 

 Aude, in the middle of a fauna essentially tertiary. 



A prodigious quantity of discoidal orbitolites found in several places, 

 characterise this formation as a ISIediterranean type ; but not even a 

 single nummulite has been as yet discovered in it, that fossil being 

 confined exclusively to the superior system. [J. N.] 



