70 BIBLIOGRAPHY AND INDEX OF N. A. GEOLOGY, [bull. 149. 
523 Norton (William Harmon). Variation in the position of the 
nodes on the axial segments of pygdium of a species of 
Encrinnrns. 
Iowa Acad. Sci., Proc., vol. iii, pp. 79-81, 1896. 
Describes Encrinnrns pnnctatus, and gives a table showing the num- 
ber of axial aunnlations in 43 specimens from the Niagara strata in 
Iowa. 
o. 
524 Ordonez (Ezequiel). Las roeas ernptivas del Suroeste de la 
cnenca de Mexico. 
Institute geologico de Mexico, Bull. No. 2, 46 pp., 1895. 
Describes the general character of the valley of Mexico, the occurrence 
of the igneous rocks, the character of the volcanoes of Santa Catarina 
and of the Sierra de la Cruces, with a discussion of their petrographic 
characters. 
525 Ortmann (Arnold E.). An examination of the arguments by 
Neumayr for the existence of climatic zones in Jurassic 
times. 
Am. Jour. Sci., 4th ser., vol. i, pp. 257-270, 1896. 
Reviews the paleontologic and geologic evidences considered by Neu- 
mayr to indicate the existence of climatic zones in Jurassic time. 
520 On separation, and its bearing on geology and zoogeography. 
Am. Jour. Sci., 4th ser., vol. ii, pp. 63-69, 1896. 
Discusses the causes of separation or isolation of animals and the evi- 
dences of its being a particular factor in the differentiation of species. 
527 Osborn (Henry Fairchild). The cranial evolution of Titanothe- 
rium. 
Am. Mus. Nat. Hist., Bull., vol. viii, pp. 157-198, pis. iii-iv, figs. 1-13, 
1896. 
Discusses the evolution of the titanotheres of the White River beds 
and describes a number of species. 
528 Patton (Horace B.). Concretions of chalcedony and opal in obsid- 
ian and rhyolite in Colorado. 
Read before the Colorado Scientific Society, in Golden, Colo., Nov. 4, 
1895, 6 pp., 2 pis. 
Describes the occurrence of the concretions and their megascopic and 
microscopic characters. 
529 Peculiar geological formations at the head waters of the Rio 
Grande, Colorado. 
Read before the Colorado Scientific Society, in Golden, Colo., Nov. 4, 
1895, 2 pp., 2 pis. 
Describes erosion forms of volcanic conglomerates. 
