32 
LACCOLITHIC MOUNTAINS 
one which is exactly synonomous with the name laccolith itself 
as now understood. Of course Iddings’ original diagram of a 
bysmalith leaves the impression of what Harker afterwards 
designated a “plutonic plug.” 
As first supposed to exist the bysmalith was regarded as one 
extreme of laccolithic development in which the vertical axis of 
the intrusive body was greatly extended; on the other hand the 
extreme development of the horizontal axis was considered as 
producing the sill or sheet as urged by Gilbert. The necessary 
consequences of the first assumption was to associate the laccolith 
with the extrusive, or volcanic, rather than the intrusive phases 
of magmatic outwelling. This tendency is shown in many if not 
the majority of the allusions to laccoliths. On the excursions 
of the Seventh International Geological Congress through the 
Caucausus -region K. Roguewitch and others among the Russian 
geologists, pointed out the eruptive masses of Piatigorsk as Euro¬ 
pean types of the American laccoliths. More recently Van de 
Derwies takes the same view. These hills, however, are mani¬ 
festly merely old denuded volcanic necks and find their nearest 
American affinities in the El Cabazon field of the Mount Taylor 
district of New Mexico. 
Relations between Bathyliths and Laccoliths. The common 
conception of a bathylith is a laccolithic blister of giant propor¬ 
tions. Unlike the laccolith the bathylith is fancied as having no 
determinable floor, which later, according to Suess may be 
entirely fused and mingled with the magma. As the central 
core of great mountain chains the granitic body is so large that 
the accompanying faulting of the overlying strata is relatively 
almost infinitesimal and the stratified formations form essentially 
true arches. To these circumstances the Gilbert notion of an 
ideal, regular laccolith exactly fits. As expressions of similar 
orographic powers laccoliths and bathyliths are clearly and closely 
related genetically. Because of a vast difference in size local dis¬ 
placement of strata largely determines the one while it has little 
or nothing to do with the other. On account of circumstances 
19 Nat. Hist, of Igneous Rocks, 1909. 
20 Guide des Exc. du VII Cong. geol. international, XVII, p. 5, 1897. 
21 Rech. geol. et petrog. sur les laccolithes des environs des Piatigorsk, 1905. 
22 Proc. Iowa Acad. Sci., Vol. VII, p. 137, 1901. 
23 Sitzunberichte der Weiner Academie, Bd. CIV, p. 52, 1895. 
