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Dike III. begins at 138 feet east of No. 2 and is but five 
feet broad. It contained merely the serpentinous earth, and was 
traced to the southward about 25 feet. 
Dike IV. is by far the most interesting of this series. It is 
the only one that contains any quantity of unaltered rock, and is 
sQ situated as to be permanently exposed on the north side of 
Green street. This is due to the lowering, some years ago, of the 
grade of the street about fifteen feet at this point. The section 
is most favorable for study, crossing the dike at right angles, and 
showing not only the dike proper, but a small branch of the same, 
an overflow spreading over the adjoining shales for some dis- 
tance, the uplifting and flexing of the adjoining shales and lime- 
stones, contacts which are most clear and distinct, and a slight 
discoloration of the immediately adjoining shales. This dike is 
25 feet east of No. 3 and is 14 feet in width in the trench. 
In this excavation there is from 18 to 24 inches on either side 
where the rock had changed to earthy matter resembling the 
material in the adjoining dikes but for fully ten feet at the center 
it was hard and firm rock. In the permanent exposure above the 
present roadway the width of the dike is more than twice its 
width in the trench. Here the exposed surface of the rock is 
much altered but back in the hillside it is quite firm. There is 
little question but that the “intruded sheet ’’ which was made 
so much of in the earlier descriptions and which led to Hunt’s 
“Chemical Precipitation Theory’ for the formation of serpen- 
tine, was derived from this dike; or, more properly, the facts 
now known seem to warrant the statement that the seemingly in- 
truded sheet was really the dike itself. The James street hillside, 
sloping to the westward, formerly exposed the edges of the hori- 
zontal layers of Salina rock. Striking northward a part way up 
this hillside is the dike. To a person climbing the hill what would 
be more natural than to suppose that this band of greenish crys- 
talline rock apparently lying between horizontal calcareous layers, 
seemingly above and below it, was the edge of some correspond- 
ing layer? Sixty-five years ago, when this rock was first noticed, 
this region was open, uninhabited, and contained little or no veg- 
itation on the slope, and the dike could be easily distinguished. 
