the
portions excavated previous to 1908 being inclosed in a dotted line. As
shown in this diagram, the Mount Mica pegmatite mass dips gently 20° to
30° SE., being intruded in general parallel to the trend of quartz-mica
schists, which at the quarry strike N. 50° to 60° E. and dip 20° to 30°
SE. The significance of certain schist fragments inclosed in the
pegmatite is discussed on page 135.
The
schists are unquestionably of sedimentary origin but are locally so
much injected by narrow sheetlike offshoots from the larger pegmatite
masses that they resemble igneous gneisses. The contact of the
pegmatite on the schist is generally very sharp and there is no
indication of any absorption of the schist, though the abundance of
garnets near the contact indicates some contact metamorphism.
The
whole pegmatite mass is not productive (see fig. <S), the gem and
pocket bearing portion constituting a zone ranging from a few inches to
6 or 7 feet in thickness lying immediately below the schist capping.
The productive layer originally outcropped at the surface, a relation
to which was due its discovery and the ease with which it was worked in
the early days. At present the southeastern wall of
