Geology and Mineralogy. 401 



7. A ring magnet for obtaining intense magnetic fields. — Very- 

 little attention has been paid to the better construction of power- 

 ful electromagnets for physical experiments. In most physical 

 cabinets will be found the Ruhmkorff magnet which was designed 

 before clear ideas of the magnetic circuit had been obtained. 

 H. DuBois has therefore designed a ring-formed electromagnet 

 by means of which experiments with powerful magnetic fields 

 can be carried out. The entire magnet constructed under his direc- 

 tion weighed between 500 and 600 pounds — between suitable con- 

 ical pole pieces a field of 40,000 C. G. S. units was obtained, over 

 a space whose diameter varied from three to five millimeters. — 

 Ann. der Physik und Chemie, pp. 537-549, No. 3, 1894. j. t. 



II. Geology and Mineralogy. 



1. The age of the White Limestones near Warwick, Orange Co., 

 N. Y~. — An examination of the geological structure, and a petro- 

 graphical study, of the white and blue ciystalline limestones and 

 associated granites of the regions about Mounts Adam and Eve have 

 been made by Messrs. J. F. Kemp and Arthur Hollick. This 

 is the northern extension of the belt of limestones described by 

 F. L. Nason in the New Jersey Annual Report for 1890 under the 

 title of " The Post- Archaean age of the white limestones of Sussex 

 Co., N. J." (see this Journal, vol. xlii, p. 70, 1891.) The authors of 

 the present paper are " on the whole forced to the opinion that the 

 white limestone is metamorphosed blue," which in its extension 

 in New Jersey contains Cambrian fossils, and think it most 

 reasonable to attribute the change to the granite intrusions. " The 

 limestones near the contact become charged with silicates, either 

 in bunches and irreglar masses or else in general dissemination. 

 These masses are chiefly brownish-green hornblende of a peculiar 

 tint, dark brown biotite or phlogopite, light green pyroxene, 

 titanite, calcite, pyrite and some scapolite. Chondrodite, at times 

 thickly charges the limestone and with it spinel. The white 

 limestone graduates into blue with transitional graphitic forms, 

 and the remote blue limestone shows no metamorphism, and the 

 same belt in New Jersey contains Cambrian fossils." The facts 

 in the case do not seem, to the writer of this article, to warrant 

 the conclusion that the white limestone is of Cambrian age. The 

 presence of Cambrian fossils in a limestone of the same region 

 but everywhere distinctly different from it in color, textm-e and 

 contained minerals, leave the presumption that it is distinct in age 

 as it is distinct in lithological character from the blue limestone, 

 so long as there is neither fossil evidence to determine any age, 

 nor continuity in the sedimentation to show stratigraphical 

 sequence. I have examined in Arkansas two examples of unal- 

 tered, stratified limestones of different geological age, appearing 

 in the same section, with only slight difference in texture, color 

 or position of bedding, which were classified by careful geologists 

 as one continuous limestone. In one case the fossils on one side 



