weeks.] PALEONTOLOGY, PETROLOGY, AND MINERALOGY, 1898. 103 
916 Winchell (Newton H.). The determination of the feldspars. 
Am. Geol., vol. xxi, pp. 12-49, 28 figs., 1898. 
Discusses methods of determining feldspars. 
917 [Review of "Volcanoes of North America; a reading lesson 
for students of geography and geology," by Israel 0. Russell.] 
Am. Geol., vol. xxi, pp. 65-66, 1898. 
918 Some resemblances between the Archean of Minnesota and 
Finland. 
Am. Geol., vol. xxi, pp. 222-229, 1898. 
Describes the succession of the Archean series in Minnesota and com- 
pares them with the Archean of Finland. 
919 The significance of the fragmental eruptive debris at Taylors 
Falls, Minnesota. 
Am. Geol., vol. xxii, pp. 72-78, 1898. 
Describes the occurrence of two beds of conglomerate and their age 
and relation to the igneous rocks. Notes similar occurrences at other 
localities. 
920 The question of the differentiation of magmas. 
Am. Geol., vol. xxii, editorial comment, pp. 113-123, 1898. 
Reviews the literature of the subject and gives the writer's views. 
921 Note on the characters of mesolite from Minnesota. 
Am. Geol., vol. xxii, pp. 228-230, 1898. 
Describes the microscopic characters of the material. 
922 The origin of the Archean igneous rocks. 
Am. Geol., vol. xxii, pp. 299-310; Abstracts, Am. Assoc. Adv. Sci., Proc, 
vol. xlvii, pp. 303-304; Science, new ser.,vol. viii, pp. 504-505 (| p.), 1898. 
Reviews previous discussions of the subject and gives the author's 
views. 
923 Thomsonite and lintonite from the north shore of Lake 
Superior. 
Am. Geol., vol. xxii, pp. 347-349, 1898. 
Describes occurrence and character of the material. 
924 The oldest known rock. 
Abstract, Am. Assoc. Adv. Sci., Proc, vol. xlvii, pp. 302-303; Science, 
new ser.,vol.viii, p. 504 (£p.), Am. Geol., vol. xxii, pp. 262-263 (i p.), 1898. 
Describes certain greenstones and associated rocks, 
925 Winslow (Arthur). A natural bridge in Utah. 
Science, new ser., vol. vii, pp. 557-558, 2 figs., 1898. 
Describes its character and origin. 
92G Wolff (J. E.). Petrography [vicinity of Boston, Mass.]. 
Am. Assoc. Adv. Sci , Fiftieth Anniversary Meeting. Guide to locali- 
ties illustrating the geology, marine zoology, and botany of the vicinity 
of Boston. Edited by A. W. Grabau and J. E. Woodman, p. 63, Salem, 
Mass., 1898. 
Gives a brief note on the petrographic features of the region. 
