  In F-theory, if a fiber type of an elliptic fibration involves a condition
that requires an exceptional curve to split into two irreducible components, it
is called ``split'' or ``non-split'' type depending on whether it is globally
possible or not. In the latter case, the gauge symmetry is reduced to a
non-simply-laced Lie algebra due to monodromy. We show that this
split/non-split transition is, except for a special class of models, a conifold
transition from the resolved to the deformed side, associated with the conifold
singularities emerging where the codimension-one singularity is enhanced to
$D_{2k+2}$ $(k \geq 1)$ or $E_7$. We also examine how the previous proposal for
the origin of non-local matter can be actually implemented in our blow-up
analysis.
