Essentially, a sill is an intrusive igneous rock body, that superficially mimics a volcanic flow.
A thrust fault is such that, it is possible for older rock layers to be physically moved to be on top of younger rock layers (opposite of the normal superposition). The upper rocks (the upper plate of the fault) are "overthrust" over the lower rocks (the lower plate of the fault).
------------------ BS degree, geology, '83 Professor, geology, Whatsamatta U Old Earth evolution - Yes Godly creation - Maybe
[This message has been edited by minnemooseus, 08-14-2002]