706 J. P. [IDDINGS 
lith. By this mode of intrusion, the vertical dimension of the 
intruded mass becomes still greater as compared with the lateral 
dimensions, so that its shape is more that of a plug or core. 
Such an intruded plug of igneous rock may be termed a dysmalith 
(Btopua = plug, Ad#os = stone). There is thena transition from 
a flat, intrusive sheet to a laccolith with lenticular form, and from 
this to a bysmalith with much greater depth and considerable 
vertical displacement. 
The resemblance of a bysmalith to a stock of igneous rock is 
such as to suggest at first their identity or close relationship. 
And though bodies of igneous rock may occur whose character 
might lead to their being classed with either of these types of 
intrusion, nevertheless it will be found advantageous to discrim- 
inate between bysmalith and stock by limiting the term stock to 
such bodies as occupy nearly vertical tubes or funnels of indefi- 
nite depth in rocks of any and all kinds, massive, schistose or 
stratified, and which maintain such a relation to them as to 
appear to belong to the category of dikes. Such tubes or funnels 
have been produced most probably by the enlargement of a fissure 
or a cluster of fissures by the carrying up of fragments torn from 
the walls. Stocks frequently represent the filling of a channel 
through which successive eruptions of magma have passed, as 
the conduit of a volcano. The formation of a bysmalith is more 
properly one act of eruption, and the solid rock removed is a 
block of nearly horizontal strata lifted at one time. 
Examples of bysmaliths have not been described as such to 
any extent so far asthe writer knows. Russell* has called atten- 
tion to what he considers volcanic plugs in the region of the 
Blacks Hills of South Dakota and has suggested their recognition 
as types of intrusions different from laccoliths. But in his des- 
cription of them he has mentioned nothing that demonstrates or 
even indicates that they possess the character of a plug. In 
each case they may be central remnants of small laccoliths. 
This is made probable by the position of the prismatic columns, 
which would be vertical in the central part of a laccolith, whereas 
LRUSSHs le Can lOURN GEOL. VOl. Vane 23s 
