232 J. F. XEWSOM — CLASTIC DIKES 



At 2, 75 feet downstream from 1, is a 10- foot dike of fractured hard 

 gray sandstone containing innumerable calcite veinlets. One of the 

 walls of this dike shows a dip of 65 degrees north 6 degrees east. This 

 intrusion crops out of the hill east of and 45 feet above the creek. 



At 3, 150 feet below 2, is a dike varying in thickness from 2 to 6 inches 

 and standing almost vertical. It has a strike of south 66 degrees west. 

 The shales here dip 20 degrees north 56 degrees east. 



At 4, immediately below 3, are three thin intrusions shown in figure 

 1, plate 21. In the picture the hammer leans against 2, the figure of 

 the man is midway between 2 and 3, and at the right of the picture 4 is 

 shown. These intrusions vary in dip from 55 to 90 degrees and in thick- 

 ness they vary from 1 to 3 inches. They are much harder than the 

 inclosing shales and stand, up above the shale like the irregular edges 

 of so many boards. 



The dike indicated at 5 is 18 inches thick ; it dips 70 degrees south 14 

 degrees east and cuts shale which dips 30 degrees north 35 degrees 

 east. This intrusion, which contains inclusions of shale, is of hard gray 

 sandstone and projects 18 or 20 inches above the shale, sand, and gravel 

 in the creek bed. 



Forty feet below 5, at 6, a 3J-inch dike dipping 80 degrees north 5 

 degrees west is exposed at the west side of the creek; it is of hard sand- 

 stone and stands out from 10 inches to 1 foot above the shale. This 

 intrusion is slightl}^ faulted. The faulting and the relations of the dike 

 to the shale are shown in figure 2, plate 21. 



At 8 is a 6-foot, vertical, hard, gray sandstone dike with man\^ calcite 

 veinlets; at 9, 4 feet below 8, is. a 22-inch intrusion standing vertically 

 and striking north 65 degrees east, and at 10, which is 4 feet below 9, is a 

 4-inch dike with shale inclusions. It is almost vertical and is parallel 

 to 9. . These dikes are exposed on the west side of the creek and outcrop 

 for a distance of about 15 feet. Figure 1, plate 22, looking west, shows 

 the relations of these intrusions to each other. 



Thirty feet below 10 a 2j-foot dike is poorly exposed at 11. 



At 12, 200 feet below 11, one of the most interesting of the Graves 

 Creek dikes is exposed on both the east and west sides of the creek for 

 a distance of about 35 feet. It is vertical, has a strike of north 70 

 degrees east, is composed of hard gra}^ sandstone, and contains shale 

 inclusions. The best exposure is in the east bank of the creek (figure 

 3). Here the intrusion is 2h- feet thick at the level of the creek bed. 

 Six feet above the waterlevel it increases to a thickness of 5 feet. 



While the shale both above and below on the creek has the ordinary 

 low northeast dip, the beds adjacent to tlie dike are tilted up and dip 

 awa}^ from the intrusion on either side at an angle of about 45 degrees. 



