Geology. 351 



of the Apps coil included a step-up transformer constructed on the 

 principle of those described by Mr. Tesla. The author thinks 

 that the assumption that high frequency currents are harmless by 

 reason of their high frequency is not correct. The true reason 

 being the extremely small amount of current which accompanies 

 the high voltage. — Phil. Mag., February, 1893, pp. 142-145. 



J. T. 



II. Geology. 



1. Correlation Papers — Neocene [Bulletin of the U. S. Geo- 

 logical Survey, No. 84, Washington, 1892) ; by William Healet 

 Dall and Gilbert Denison Harris. — A part of the recent 

 work of the Geological Survey in the classification of the forma- 

 tions of the United States for the purpose of constructing a gen- 

 eral geologic map is represented by a series of memoirs showing 

 the present state of our knowledge of the several systems of 

 rocks, in America, the series being called " Correlation Papers." 

 The memoirs represent not only bibliographic study but more or 

 less field work. That pertaining to the Neocene (including the 

 Pliocene and Miocene of the Lyellian classification) is especially 

 rich in results of original field researches in both invertebrate pale- 

 ontology and stratigraphy. The treatment of Florida and Alaska 

 in particular is monographic, and so largely based on the personal 

 observations of the senior author as to render the memoir the best 

 source of information extant concerning the geology of these little 

 known corners of our domain. 



The Neocene formations of the country are considered as be- 

 longing to three natural geographic provinces, viz : the Atlantic 

 and Gulf province, the Pacific coast province, and an interior 

 province made up of terrestrial and freshwater basins. The prin- 

 ciples of classification recognized are far-reaching and philosophic. 

 In the first place, the deposits are classified bv genesis as (1) 

 marine sediments, (2) perizonal deposits (the deposits accumu- 

 lated " between the neuti-al zone where sediments are dropped " 

 by the sea " and the point where subaerial erosion terminates " — 

 page 98), (3) lake beds, and (4) subaerial and fluvial deposits. 

 These several classes of deposits are regarded as dynamic types. 

 Proceeding on the basis of this physical classification, the applica- 

 tions and limitations of paleontologic correlation are next set 

 forth. It is first shown that deposits of different dynamic types 

 may be synchronous, as the life conditions are sometimes so di- 

 verse that synchrony can neither be assumed nor denied a) priori. 

 Then the more general conditions affecting deposition and organic 

 existence are discussed, and it is shown that the distribution of 

 fossils and thus the correlation of fossiliferous formations is af- 

 fected by various conditions, notably sea-temperature. From a 

 census of the shell-bearing marine mollusks in recent faunas of 

 different temperature zones throughout the world, the authors 

 " conclude that that part of the average mollusk fauna which is 



