Granitindustrien ved Idefjorden
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Forkortet: The Iddefjord is the south-eastern part of Norway at the Swedish border. The granite there is of middle grain and gray (sometimes a little reddish). The rock is to a certain degree cleavable in two directions, standing at right angles to one another. One of these cleavage-structures is far better than the other, but only of the better one there is a faint trace visible to the experienced eye in the outer appearance of the rock. The principal cleavage (dotted lines in the fig. showing the manner of quarrying p.74) lies in our district rather horizontal. The most important system of joints (b and the face a in the fig.) is in the quarrying region of Krokstrand dipping at a small angle toward the horizontal plane and in this manner not quite concordant with the cleavage. It is a common observation, that the joint-system in the quarries dips in the same direction as the outer surface of the ground, a fact already observed here by Prof. J.H.L.Vogt.