Geology and Mineralogy. 317 



invasion of short duration, for during Lower and Middle Jurassic 

 times Mexico appears to have been land. This fact may 

 explain the very isolated occurrence of the Triassic fauna as a 

 preserved remnant of a wide removal during the land interval. 

 Over it repose marine strata of Upper Jurassic age, and from 

 that time to the close of the Mesozoic, Mexico was apparently 

 continuously beneath the sea. c. s. 



15. La Favne Jurassiqice de Mazapil ; par Carlos Burck- 

 haedt. Boletin 23, Inst. Geol. de Mexico, 1906, 192 pp., 43 pis. 

 — This work should be studied in connection with G-eologie de la 

 Sierra del Mazapil et Santa Rosa • by Carlos Burckhardt. 

 Guide Geol. au Mexique, Tenth Internat. Geol. Congress, 1906, 

 pt. xxvi. 



In this handsome and welcome quarto volume are described 85 

 (45 new) species of ammonites in 16 genera (Ldoceras new). Of 

 these, 7 are definitely identified with central European forms 

 (Opellia flexuosa costata, Aspidoceras contemporaneum, A. bispi- 

 nosum, Ldoceras laxevolutum, L bcddernm, LLaploeeras filiar, 

 Phylloceras apenninicum), 1 with the boreal fauna of Russia 

 (Perisphinctes ni/citini), 2 with India (at Spiti, Aspidoceras 

 arelhmoides, LLaploeeras ordonezi), and 1 in the Cordilleras of 

 Argentina (Aspidoceras cyclotimi). There are likewise 14 species 

 more or less closely related to forms from other regions. Of these, 

 11 go with central European regions and 3 with Argentina. 



The Upper Jurassic strata of the Santa Rosa and Caja Moun- 

 tains about Mazapil in the State of Zacatecas are well developed. 

 These are divided into two main groups correlated with the 

 Kimmeridgian and Portlandian of Europe. The former is again 

 divided into four zones, — shales with Waagenia, zone of Haplo- 

 cerasjiliar, zone of Aitcella pallasi mexicana, and basal zone of 

 Ldoceras, while the Portlandian is divisible into three zones, — 

 whitish calcareous shales with LLoplites of the group Calisto, 

 gray phosphatic limestones, and red phosphatic limestones with 

 Aspidoceras cyclotum and Perisphinctes cfr. danubiensis. The 

 thickness of these strata appears not to exceed 260 feet. 



The general aspect of the ammonites here described reminds 

 one greatly of those of central Europe. This is seen not only in 

 the species common to the regions on both sides of the Atlantic, 

 but also in the identical succession of the faunas. In comparing 

 the formations of Mazapil with those of southeastern France, the 

 author states : "The analogy of the Mexican series with that of 

 Europe is striking. In both cases, above the Lower Kimme- 

 ridgian there are deposits with a great development of LLaploee- 

 ras filiar and Oppelia of the group of 0. flexuosa. In the two 

 regions the remarkable genus Waagenia also appears in the 

 higher beds, and these in turn are overlaid, in Mexico as well as 

 in France, by the zone with Oppelia lithographica and by the 

 Lower Portlandian" (178). The fact that the Mazapil ammo- 

 nites also have affinities with those of the Cordilleras of Argen- 

 tina is not thought to indicate a direct communication between 

 this area and Mexico. c. s. 



