Woodworth.— Joints. 
PLATE 1. 
Fig. 1. Diagram of feather-fracture as exhibited on joint-plane cutting a 
stratum whose upper and lower surfaces form the edge of the 
joint-plane. See p. 165. 
Fig. 2. Diagram of side of a joint-block with twinned feather-fracture and 
two axial planes. Mystic River quarries. See p. 167. 
Fig. 3. Diagram of the four sides of a joint-block drawn as if lying in one 
plane. The lines covering the interior square or surface of the 
joint-block represent shading only. Mystic River quarries. Seep. 168. 
Fig. 4. Intersection of two joint-planes, slightly departing from a common 
plane. The plane on the right probably continued in the rock to the 
left and was later cut by the joint-plane on the left. 
Fig. 5. Joint-plane with fringe, showing relation of feather-fracture to frac¬ 
ture system in the fringe, dd, edge of the joint-plane; bb, border- 
planes of the fringe; cc, cross-fractures. 
Fig. 6. Diagram showing direction of main joint-plane and border-planes 
of the fringe. In ridges and ranges of secondary structures of 
large size, the straight line would correspond to the main trend 
of the mountains or volcanic group. Such trend lines are more 
often curved. 
Fig. 7. Plan of border-planes prior to formation of cross-fractures in joints. 
See p. 171. 
Fig. 8. Diagram showing relation between border-planes and cross-fractures. 
bb, border-planes; cc, cross-fractures. 
Fig. 9. Distribution of feather-fractures on border-planes. 
Fig. 10. Ideal scheme of elliptical joint in stratified rock, a, center of figure 
of the fractured surface; bb, border-planes of the fringe; b' b', distal 
border-planes, often extending from upper to lower limits of the 
joint-plane. (See Plate 5, fig. 1.1 cc, cross-fractures; dd, edge of 
joint-plane, and inner margin of the fringe; ee, axis of feather-frac¬ 
ture, parallel with the stratification. Outside of the fringe here 
represented there may occur a rim of conclioidal fracture, or this 
may replace the fringe and begin at the edge of the joint-plane. 
See p. 173. 
