BYSMALITHS 709 
a much higher horizon in the sedimentary terrane. ithe total 
thickness of beds, that were most probably superimposed on the 
gneiss at the time of the eruption under discussion, is about 9000 
feet. These were lifted more than 2300 teet, possibly 4000 feet, 
and the position of the strata after the intrusion may have been 
similar to that shown in the accompanying figure, which corres- 
ponds in scale to the Holmes bysmalith. The section passes 
through Mount Holmes and Echo Peak, and does not intersect 
the conduit. 
A more complex body of igneous rock closely related to a 
bysmalith occurs six miles farther north in the Gallatin Moun- 
tains at Gray Peak. It has broken across the strata and has 
forced into them numerous sheets of igneous rock. It is 
exposed at a much higher horizon than the Holmes bysmalith, 
cutting the Dakota conglomerate of the Cretaceous. Its posi- 
tion with regard to adjoining strata is not so well shown as in 
the case first described, however enough is exposed to prove its 
plug-like character. 
It is probable that this type of intrusion will not be found 
to be as frequent as the laccolith, just as the latter is much less 
common than the intruded sheet. 
The term dathylith has been proposed by Suess’ for an intruded 
body having a more or less lenticular shape, which he considered 
to have been formed by intrusion of molten magma into a previ- 
ously existing cavity made by the crumpling of the earth’s crust. 
But, as Zirkel? has pointed out, the only difference between 
the bathylith of Suess and the laccolith of Gilbert lies in their 
mode of formation, their shapes being similar. It is questionable 
whether bathyliths defined in this strict manner exist. Indeed 
they probably do not. There has been a tendency among 
American geologists to use the term bathylith in a different 
sense from that in which Suess originally used it. This has been 
expressed by Dana? in his Manual of Geology in discussing the 
«Suess, E., Das Antlitz der Erde. Vienna, 1892, p. 219. 
2 ZIRKEL, F., Lehrbuch der Petrographie. Leipzig, Vol. I, p. 548. 
3DaNnaA, J. D., Manual of Geology, Fourth Edition, 1895, p. 811. 
