LACCOLITHIC MOUNTAINS 
33 
of this kind such classifications of intrusive rocks as that recently 
proposed by Professor Daly utterly fail in the genetic element. 
Bathyliths, laccoliths and bysmaliths are placed in distant cate¬ 
gories fundamentally removed from one another whereas genetic¬ 
ally they constitute a single ’order. It is notorious that the basal 
plane of laccoliths crosses the bedding planes of the intruded 
strata as often as it coincides with them. As shown in the Ortiz 
intrusive a bysmalith is about as far removed from a volcanic 
neck as it is possible to have it. 
Formative Relations of Laccoliths. As laccolithic masses come 
to be more and more carefully scrutinized theoretical considera¬ 
tions begin to point more and more to the circumstance that im¬ 
mediately prior to intrusion distinctive tectonic conditions and 
especial stratigraphic structures must constitute more important 
determining causes. What appears to be usually mistaken for 
evidence of hydrostatic pressure of the magma is in reality oro¬ 
graphic potentiality of the same category as flexing in mountain 
building. The magma itself seems to play merely a passive role. 
Perusal of the literature on laccolithic themes, published during 
the past 30 years, since the date when the term was first fixed 
as applying to a distinctive conception likewise shows that with 
constantly increasing frequency reference is made to displacement 
as an accompaniment of this particular type of intrusion. 
Recent critical examination of the broader structural features 
of some of the New Mexican laccolithic mountains seems to con¬ 
nect directly the intrusion of the eruptive masses with not only 
contemporaneous faulting but with both more anciently acquired 
regional tectonics and profound displacement dating some little 
time prior to the main accumulation of magmatic materials. 
A number of facts militates strongly against the Henry Moun¬ 
tains explanation of laccolithic protuberance. Three basic prem¬ 
ises appear wholly untenable. Most vitiating is the seeming in¬ 
competency of simple hydrostatic pressure to produce the desired 
results. Inadequacy of relative lithologic density is now common¬ 
ly conceded. There also appears to be a radical disparity between 
the physical conditions accompanying ^he formation of laccoliths 
and their once supposed nearest kin the sills. 
On the other hand the recent unearthing of the infrabasal 
make-up of certain laccoliths clearly points to a fundamental 
