ology and Mineralogy, 235 



AbsohiU Measurements in Electricity and Magnetism by 

 Andrew Q-bay. Second Edition revised and greatly enlarged. 

 384 pp. 1 2 mo. London and New York, 1889. (Macraillan <fc Co.) 

 A first edition o( this work was published in L884, (this Journal, 

 vol. rxvii, 487): Bince that time the author has issued the first 

 volume of a larger and more exhaustive work on the theory and 

 practice of Absolute Measurements In Electrioity and Magnetism, 

 a second volume oi' which is now in press. Excellent as is this last 

 mentioned work, it does not take the place to the student of the 

 more elementary one which preceded it. It is well therefore 

 that the author has been induced to revise the latter; in its 

 present expanded form th<> student will find it a most satisfactory 

 guide to the methods of quantitative measurement which form the 

 foundation of modern electricity. 



io. Elementary Lessons in Electricity and Magnetism, by Sil- 

 vanus P. Thompson. 456pp. l2mo. London and New York, 1889. 

 (Macmillan A: Go.) The first publication of this admirable 

 little book was noticed in vol. xxiii, of this Journal. Since that 

 time it has been repeatedly revised and the present issue is of 

 the forty-third thousand. No better proof than this remarkable 

 reception is needed of the excellence of the work and of its 

 adaptation to the wants of the particular class of students for 

 whom it was prepared. 



II. Geology and Mineralogy. 



I. Sedgwick and MurcAison, page 167. — It is a pleasure to 

 announce that the paper of Murchison published in the Philo- 

 sophical Magazine for July 1835, is republished in the American 

 Geologist for February. 



With regard to the Lower Silurian, the terra Cambro- Silurian, 

 which is used already by the Canadian Survey, might serve, 

 supposing another name needed, if its signification accorded with 

 geological usage. It means, as employed in Canada, a formation 

 that is neither Cambrian nor Silurian, but which lies between the 

 Cambrian and Silurian formations. This is out of harmony with 

 the terms Permo- Carboniferous, Jura-Trias, Calciferous- Trenton, 

 and the like; which stand for combinations of' the formations 

 indicated, and especially where their separation is at present diffi- 

 cult or impossible. Such terms are too useful in the science to be 

 dispensed with. j. D# D . 



2. The Calciferous Formation in the Champlain Valley, 

 Xotes from a paper presented before the Geological Society of 

 America, at its winter meeting, Dec. 26-28, 1889, by E. Brainerd 

 and II. M. Seely. — The region under investigation extends east 

 and west from the flank of the Green Mountains to the Adiron- 

 dacks, a distance of about twenty miles, and north and south 

 from Phillipsburgh, Canada to Benson, Vt., and Ticonderoga, 

 N. Y., near eighty miles. 



In this valley all the formations of the Lower Silurian are rep- 

 resented. On the east the rocks are much metamorphosed ; on 



