CLASSIFICATION OF IGNEOUS INTRUSIVE BODIES 501 



true laccoliths and typical "chonoliths," but belong to the latter 

 class rather than to the former. Jaggar also describes the "False 

 Bottom Stock" of phonolite in such terms as to lead one to suspect 

 that it may be another, perhaps typical, body of the " chonolith" class. 1 



Jaggar, 2 collaborating with Howe, has experimentally reproduced 

 the conditions under which some "chonoliths" have originated; 

 namely, such bodies as have been injected primarily through the 

 application of force resident in fluid magma under pressure (hydro- 

 static force). No attempt was made, in their valuable experiments, 

 to imitate injection concomitant with regional deformation. 



Whatever may be the validity of any or all of these several cases 

 as illustrations of "chonoliths," there is no question that they can 

 be called "stocks" or "laccoliths," or by any other of the established 

 names, only at the sacrifice of much of the strength, precision, and 

 usefulness of those names. On the other hand, there are thousands 

 of irregular injected bodies which cannot properly be described by 

 the use of any of the established names. It is to be noted, finally, 

 that some such term as "chonolith" may be useful in suggesting the 

 probable nature of an intrusive body in the case where its whole 

 form is not certainly known. The context should then, of course, 

 indicate that the author using the term has in mind only a probability 

 and is making, as it were, simply a report of progress in the description 

 of that particular body. 



Boss. — A Geikie 3 defines bosses as 



masses of intrusive rock which form at the surface rounded, craggy, or variously 

 shaped eminences, having a circular, elliptical or irregular ground plan, and 

 descending into the earth with vertical or steeply inclined sides. Sometimes 

 they are seen to have pushed the surrounding rocks aside. In other places they 

 seem to occupy the place of these rocks through which, as it were, an opening 



has been punched for the reception of the intrusive material In true bosses, 



unlike sills or laccolites, we do not get to any bottom on which the eruptive material 

 rests. 



He makes "stock" and "boss" synonymous. 



In his Text-book 4 Geikie says: "Bosses (stocks) are amorphous 

 masses that have disrupted the rocks through which they rise." 5 



1 Ibid., p. 227. 3 Ancient Volcanoes, Vol. I (1897), p. 88. 



2 Ibid., p. 302, and Plate 43, section 2. 4 Vol. II (1903), p. 722. 

 s Cf. also A. Geikie, Geology oj Eastern Fife (1902), p. 189. 



