♦720 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



such bodies may be due to a combination of the two primary causes — orogenic 

 stress opening cavities, and hydrostatic or other pressure emanating from the 

 magma itself and widening the cavities. 



No generally accepted name has yet been proposed for such irregular 

 intrusions. ' Laccolith ' cannot be used, since that term denotes a definite form,- 

 and also implies a special mode of intrusion different from that here conceived. 

 The writer has not been able to find a simple English word for the purpose, 

 and suggests a name formed from the Greek on the analogy of 'laccolith/ 

 ' bysmalith,' and ' batholith.' It is ' chonolith ' derived from ^coyos, a mould 

 used in the casting of metal, and Xidos, a stone. The magma of a ' chonolith ' 

 fills its chamber after the manner of a metal casting filling the mould. Like 

 a casting, the ' chonolith ' may have any shape. 



A 'chonolith' may be thus defined: an igneous body {a) injected into 

 dislocated rock of any kind, stratified or not; (&) of shape and relations irre- 

 gular, in the sense that they are not those of a true dike, vein, sheet, laccolith, 

 bysmalith, or neck; and (c) composed of magma either passively squeezed into 

 a subterranean orogenic chamber or actively forcing apart the country-rocks. 



The chamber of a ' chonolith ' may be enlarged to a subordinate degree 

 by contact fusion on the walls, or by magmatic ' stoping.' 



Examples of ' chonoliths ' are described on pages 368, 401, 418, and 499, 

 and many bodies of this class have been mapped and sectioned in works dealing 

 with the western Cordillera of the United States. 



It may be specially noted that this new term may be useful in suggesting 

 the probable nature of an injected 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. 



Ethmolith. — The ethmolith (funnel-shaped stone) of Solomon is one of the 

 many conceivable species of chonoliths. He considers that the tonalite mass 

 of Adamello is an example. At the present erosion-surface the surrounding strata 

 dip towards the tonalite on every side and he concludes that they converge,, 

 underground, so as to cut off the igneous body except for the narrow dike, or sill- 

 feeder of the injection. On the other hand the body is supposed to have 

 enlarged to its rather flat roof, the whole form simulating a funnel. If the 

 field diagnosis be correct, the tonalite is to be regarded as an injected mass,- 

 partly cross-cutting the strata and thus has chonolithic relations.* 



Subjacent Bodies. 



Boss. — A. Geikie + 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 



* Cf . W. Salomon, Sitzungsberichte der koniglichen prenssischen Akademie der 

 Wissenechaften, Phys.-MSath. Class©, Vol. 14, 1903, p. 310. 

 t Ancient Volcanoes of Great Britain, Vol. I, 1897, p. 88. 



