JOINTED STRUCTURE. 
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145. 
View of the Cliffs on Fall creek. From a sketch by Mr. E. N. Horsford. 
CHAPTER IX. 
Jointed Structure of the Rocks of the Fourth District. 
In addition to the slaty cleavages which separate the rocks of the Fourth District into 
laminae parallel to the planes of deposition, and those lines of separation which divide the 
siliceous and calcareous masses into thicker blocks, we have another series of divisional 
planes, for the most part vertical to the line of deposition, and often penetrating to great 
depths, as seen in high cliffs and river banks. These lines of division have two directions, 
crossing each other, generally, in slightly oblique angles; though there are cases where the 
direction is nearly rectangular, as in the conglomerate, which is divided into huge blocks, 
often separated several feet from each other. 
Where these joints are numerous, they divide the rock into blocks of convenient size for 
quarrying, with vertical faces of great regularity; and where the blocks are too large, they 
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