JULY 7, 1899. ] 
Nevada had been produced by rising granite 
cores, which might or might not have reached 
the surface or been exposed by erosion. So far 
as facts in support of this theory were instanced 
by Professor Russell for regions that had come 
under the speaker’s observation, Mr. Emmons 
said they were not correctly stated or inter- 
preted, and that Russell had apparently taken 
his ideas with regard to the Colorado moun- 
tains rather from the early reconnaissance ob- 
servations of Hayden than from what had been 
written since in the light of modern geological 
research. It was only during the past summer, 
however, that an opportunity had presented to 
verify the personal observations in the north- 
ern Black Hills, upon which Russell based his 
original discovery. A detailed survey of this 
region is in progress by members of the U.S. 
Geological Survey, under Mr. Emmons’s gen- 
eral supervision, the results of which, though 
not ready for publication, show that Russell’s 
own observations, which were confined to three 
outlying groups of hills, were inaccurate. His 
supposed plugs are either laccoliths or rem- 
nants of laccolithic sheets left by erosion. In 
describing the other occurrences to support his 
plug theory Russell had relied mainly on the 
reconnaissance observations of Winchell and 
Newton made 25 or 30 years ago, before lac- 
coliths were known, and paid little attention to 
later observations. In point of fact, the region 
presents a most remarkable variety of typical 
laccoliths, and nothing corresponding to the 
supposed plutonic plug has yet been observed 
_ there. Russell’s further statement in support 
of the plug theory, ‘that dikes and faults are 
wanting in the region,’ is equally without basis 
of fact. Crosby, in the article casually referred 
to by Russell, speaks of the abundance of dikes 
in certain localities, and observation has shown 
that both dikes and faults are so abundant in 
the central mining region that they could 
hardly escape notice. 
The speaker thought such hasty generaliza- 
tions were objectionable as establishing an un- 
deserved priority in terms that when accurately 
defined and applied to observed phenomena 
might be useful to field geologists. 
This paper was followed by one upon Lac- 
coliths and Bysmatiths, by Walter Harvey Weed, 
SCIENCE. 
25 
the subject being a sequel to that previously 
discussed. The facts upon which the paper 
was based related mainly to the igneous intru- 
sive mass of the Little Belt Mountains, of Mon- 
tana, in which careful areal surveys have been 
made, but supported by observations made for 
ten years past in neighboring parts of the State. 
These intrusions commonly occur in Cambrian 
shales, and rest upon crystalline schists. They 
present gradations from intrusive sheets to 
laccoliths, and from these to asymmetric lac- 
coliths. Incidentally, it was shown that the 
asymmetry is due to the general range uplift, 
furnishing a line of weakness along the limb or 
monoclinal of the fold. Several of the intru- 
sions are, however, unlike the laccolith, unless 
Wwe assume an asymmetry about the entire cir- 
cumference. In other words, faulting and uplift, 
and not folding, is the prevailing structure. As 
the field observations show the same spreading 
out on a definite floor as in the case of the lac- 
colith, these intrusions are not stocks or the 
so-called plugs of many writers, a term lately 
revived under the title of Plutonic Plug by 
Russell. Moreover, gradations occur between 
them and the asymmetric laccolith. 
For such intrusions Professor J. P. Iddings 
has recently proposed the name of bysmalith. It 
is clearly a form heretofore embraced under the 
more general term of ‘stock.’ Its usefulness 
consists in its affording a definite name for a 
definite type of intrusion, of which several ex- 
amples have now been observed. 
From a study of the facts observed in the 
field, it appears that there is a definite relation 
between these different forms of intrusion, and 
the form is a function of several factors. The 
other factors being equal, and lines of weakness 
absent, a bysmalith has a larger floor area than 
the laccolith, which accords with the hypothesis 
that owing to viscosity of the intruding magma 
the pressure in large masses is imperfectly 
transmitted laterally, resulting in an increased 
upthrust producing faulting and the punching 
upward of the strata. Such intrusions have 
been described by Davis and Lindgren, though 
no name was given them. As the term lacco- 
lith is preferable to stone cistern, so bysmalith 
is preferable to plug-stone, both having special 
meanings not implied by the English transla- 
