248 J. F. NEWSOM CLASTIC DIKES 



12 degrees south ; at the north side the dip is 12 degrees south, 40 degrees 

 west. 



Figure 2, plate 28, is from a photograph looking northward, and taken 

 from the point X, figure 10. It shows the southwest end of the dike. 

 Plate 29, and figure 1, plate 30, are from photographs and show details 

 of the southwest end of the intrusion, taken near Y, figure 10. 



It seems, to the writer that the only possible explanation of the 

 structural features found in the large Respini Creek dike is that of in- 

 trusion of the sand from below along with water or petroleum. 



The vertical columns apparently represent the channels through which 

 ascending currents of petroleum * or water or both brought the sands from 

 below, and from which those sands were poured out at the sides, forming 

 the apparent flowage lines. It is believed that the whole mass was built 

 up in this way, and that the bands exposed on the face of the cliff at the 

 present time are merely the exposed edges of the layers which were de- 

 posited in the water around the ascending current. It is evident that the 

 mingling of the material from many ascending currents would produce 

 a complicated structure, and only under the most favorable circum- 

 stances would a simple deposit be built up of successive layers in its 

 outer portion, and with a structureless mass or plug of sand at its axis. 

 It is evident also that the sand remaining in the channels when these 

 finally became choked would not be composed of bands, but (if it were 

 not entirely structureless) would probably be columnar.t 



At 52, just north of the mouth of Respini creek, is a large V-shaped 

 sandstone intrusion, with a width of 190 feet at the top of the sea-clifl", 

 which is 45 feet high, and a width of 30 feet at the bottom. It is com- 

 posed of light brown and gray sandstone in alternating layers or bands 

 varying in thickness from 1 to 2 or 3 inches. The entire surface is given 



*In this connection the notes of Mr Henry M. Cadell on the mud volcanoes of the Irrawaddy 

 valley, in India (the Scottish Geographic Magazine, vol. xlvii, pp. 2G3-265), are of interestand sug- 

 gestive of one way, at least, in which clastic intrusions may be formed. These volcanoes are not 

 produced by steam, but, according to Mr Cadell, "are due to the escape of carburetted hydrogen 

 from the oil-bearing strata on the top of the anticline, which rises througli the clay beds, mixed 

 with a little water and oil, and slowly bubbles up at certain spots. As the gas and water rises, it 

 brings up a little gray mud, which, on exposure to the air, dries and hardens, while the water 

 evaporates, producing first a low crater basin with a dry rim of mud, then a cone with a crater on 

 the top, in the center of which the gas finds vent." 



fin order to note the phenomena of sand depositing from an ascending current of water, a box 

 with a glass side and with a three-fourths inch opening in the bottom, through which water could 

 be supplied under varying pressures, was made by the writer. Sand was then supplied to the as- 

 cending current. As sand was supplied a deposit was built up until the box was filled with a mass 

 of sand with a crater at its top, and at its center a vertical neck which finally became choked with 

 sand as the current was shut off. The layers of sand in the mass which had been built up as a 

 crater deposit sloped toward the center. The diameter of the top of the crater varied with the 

 strength of the current, being greater when the current was strong, and less when the current was 

 weak. Miniature conditions very similar to those observed in portions of the large Kespini Creek 

 dike and the dike at 52 (next to be described) were produced. 



