New Featurefi in Geology of Jlinnesota. — Winchell. 47 
the great granitic boss, and some of them being pegiuatyte, 
and hence, since peguiatj'te cannot be considered as of erup- 
tive origin, owing to tlie size of the crystals of whicli it 
consists, botli the finer and tlie coarser are to be referred to 
chemical origin. 
If now we connect these facts with the facts that are asso- 
ciated directly witli the great granitic boss which lies adja- 
cent we are almost driven to infer that the great granite area 
must have had a similar origin under more intense action of 
the same forces. These facts are :" 
1. Numerous dikes of true intrusion in the schists. 
2. Occasional inclusions of schist in the granitic mass. 
3. The sameness in character of these dikes and of the 
main boss, and of the granitic parts of the schist. Thissim- 
ilarit)'^ is general. There are variations in both. 
In general, it may be said that all this change of the schist 
to granite, or to gneiss, took place at considerable depth be- 
low the surface, and that these relations are now apparent at 
the surface because of the decay and removal of much super- 
incumbent rock. It was a process of long duration, involving 
thousands of years. It took place when the internal heat of 
the earth was much greater, and the fusing-point isothermal 
ran nearer the surface. It was at a time also, in all proba- 
bility, when the oceanic water covered the region with a thin 
aqueous layer, and when water found frequent access to the 
heated interior by reason of more frequent fractures and up- 
heavals in the thin crust. Hence heated steam was abundant 
and available to assist in the transformation of the early sed- 
iments into crystalline forms. Once plastic or molten, such 
materials would flow easily, and as soon as the}'- began to flow 
they constituted true igneous rock, in the ordinary accepta- 
tion of that term. It will be only a rare circumstance to find 
such fused rock-matter re-crystallizing again in its original 
place. It would move, in large masses and in small, and would 
make, as it does, innumerable "contacts" on the original 
schists, thus appearing to be always non-conformable. Such 
contacts^ however, are not ordinary igneous contacts, for the 
enclosing rock is nearly of the same composition, and the same 
coarseness as to crystallization as the enclosed rock, indicat- 
ing nearly the same temperature. When a molten rock con- 
