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IOWA ACADEMY OP SCIENCES 
Haworth, Winslow, and one or two others, but they have 
not received the attention they deserve, since they are nowhere 
surpassed as examples of certain phases of secular decay of 
massive rocks. The best locality known is at Granitville, a few 
miles southwest of Iron Mountain. 
The early references to the crystalline rocks of this region 
allude to a peculiar though imperfect bedding observable in the 
different exposures ; and it is probably this fact more than any 
other that leads to the general belief that most of the rocks were 
highly metamorphosed sedimentaries. This imperfectly devel- 
oped stratification, which is apparent in the granites and por- 
phyries, and in other regions in other massive crystallines also, 
arises in two ways. In the first place, the Missouri massive 
rocks are thought to be, in part at least, ancient effusivesor vol- 
canics. They are presumably great masses of lava which have 
been poured out upon an old land surface, or perhaps built up 
in shallow waters. Almost every exposure throughout the 
region reveals the presence of seams which impart to the rock 
a rude stratified appearance. Planes of this kind are widely 
known in volcanic rocks, and in almost all massive formations 
which have cooled from the molten state. In the case of effu- 
sive masses a decided lamination is frequently produced by suc- 
cessive flows which follow one after another at sufficiently long 
intervals to admit of a cooling and a partial solidification to 
take place at the surface of the different outpourings. Planes 
of separation are also commonly formed through contraction in 
cooling. Volcanic rocks also show a slight difference in chem- 
ical and mineralogical composition in different parts, which gives 
rise to a banding. When cooling takes place the difference in 
composition gives rise to divisional planes more or less parallel 
with one another, and also parallel with the surface. 
The second way in which the pseudo- stratification planes 
have developed in the massive rocks is through crustal move- 
ments. Elevation of large areas as the result of orogenic 
pressure produces great stress, which must be relieved. Fold- 
ing, faulting, and slaty cleavage are the results when the pres- 
sure is very great; only jointing and false stratification arises 
when the strains are small. The effects are very different with 
different rock masses. If the body of the rock is hard and brit- 
tle, as in the case of quartzites — the Sioux quartzite of north- 
western Iowa is a good example — the blocks are small, often 
scarcely a foot each way. If the rock is granite, diabase or 
