CLASSIFICATION OF IGNEOUS INTRUSIVE BODIES 491 



Contemporaneous vein. 



Forms part of the igneous rock in which it occurs, but belongs to a later 

 period of consolidation than the portion into which it has been injected. 1 



Apophyses or tongues are dikes or veins which, either directly or 

 by inference from field relations, can be traced to larger intrusive 

 bodies as the source of magmatic supply for dike or vein. 2 



Intrusive sheet. — This familiar expression has generally been 

 defined as equivalent in meaning to "sill." 3 It may well be extended 

 to cover the case of an igneous layer injected on a plane of uncon- 

 formity in stratified formations, when the igneous layer is thus 

 sensibly parallel to the bedding-planes of one of the stratified forma- 

 tions. This type, for lack of a better term, may be called an inter- 

 jormational sheet. For illustration of such a sheet on a colossal scale, 

 see "Map of Northern Nickel Range," Sudbury District, Ontario, 

 by A. P. Coleman. 4 



Sill. 



I. A. Geikie: 5 



A sill is a sheet of igneous material which has been injected into a sedimentary 

 series and has solidified there, so as to appear more or less regularly intercalated 

 between the strata. 6 



II. T. A. Jaggar.? 



A sill is an intrusive sheet forced between strata which are horizontal or 

 which, if tilted, lie at angles more nearly horizontal than vertical Tran- 

 sitions between dike and sill occur when a sill breaks upward at an angle of 45 , 

 or when a dike follows the bedding-planes of strata inclined at that angle. 



III. Chamberlin and Salisbury: 8 



If the lava is forced between beds of rock in the form of a sheet, and solidifies 

 there, it is called a sill. 



The definition of I and III is that which is adopted by nearly all 



1 Geikie, op. cit., p. 738. 



2 See A. Geikie, Quarterly Journal of the Geological Society, Vol. L (1894), p. 222, 

 and Ancient Volcanoes of Great Britain, Vol. II (1897), p. 439. 



3 E. g., Jukes, Manual, p. 254; Gilbert, op. cit., p. 20; Iddings, Twelfth Annual 

 Report of the U. S. Geological Survey, Part 1, p. 578; Geikie, Text-book, p. 732. 



4 Report of the Bureau of Mines, Ontario, 1904. 



5 Geology of Eastern Fife (" Memoirs of the Geological Survey of Scotland," 

 1902), p. 189. 



6 Cf Geikie, Text-book, p. 732. 7 Op. cit., p. 172. 8 Op. cit., p. 476. 



