ARRANGEMENT OF MICA IN THE DIKES. 427 



The biotite is in irregular scales, often much tattered and torn in the 

 process of transportation. As has been already noted, it is usually arranged 

 parallel to the sides of the dikes. The scales stand on edge evidently — a 

 position which they did not assume under the influence of gravity alone. 

 Thin sections of the dike rock have been prepared in three directions at 

 right angles to one another. One section was made parallel to the side of 

 the dike; the others transverse to it, both vertical and horizontal. The sec- 

 tions parallel to the sides of the dike show no conspicuous arrangement of 

 the particles, but the scales of mica are all seen broadside. In the trans- 

 verse sections, both horizontal and vertical, the biotite is seen edgewise, 

 appearing in narrow strips which are strongly pleochloric and full of cleav- 

 age lines. In the vertical transverse section the alignment of the mica scales 

 conies out most conspicuously, and in this it may be seen that all the other 

 mineral fragments in which one diameter is decidedly larger than the others 

 have their longest diameters all parallel — an arrangement which may at once 

 recall the fluidal arrangement of feldspar and other minerals commonly ob- 

 served in eruptive igneous rocks. 



Some of the scales of mica have been crushed edgewise in such a manner 

 as to cause the folia to separate and form small cavities which have since 

 been filled with calcite, the chief cementing substance of the rock. This 

 peculiarity of the mica scales is represented in figure 5. It shows that there 

 was motion in at least one of two directions, but does not distinguish between 

 them. In other cases, however, there is evidence tending to show more defi- 

 nitely the direction of motion in the sand. In figure 6 a scale of mica 

 is represented in which the folia upon the left side of the scale have been 

 crumpled by the movement of impinging grains of sand. The right-hand 

 portion of the scale has not been crumpled, and the relations of the various 

 parts of the scale suggest that the direction of motion was from below 

 upwards. 



The scales of biotite in the dike i*ock are apparently identical in every 

 way with those in the dioritic rock which is exposed northeast of Ono and 

 forms so large a part of Bally and the Trinity mountains. This view is sus- 

 tained by the presence in section 1987 of a grain of diorite in which the 

 plagioclase feldspar and biotite are well represented. 



Much of the quartz, as already remarked, comes from a similar source, 

 and so may the feldspar ; but there are many grains of a different charac- 

 ter. There are grains of serpentine and other rocks which are distinctly 

 metamorphic, like some of those of the Coast range. The commonest grains 

 are composed chiefly of fine aggregate quartz in which thei*e are minute 

 black particles, often arranged in irregular patches or streaks. They are 

 rarely clear and transparent, but frequently nearly so where microscopic 

 veins of aggregate quartz cut across the larger grains. This sort of mate- 

 rial forms a considerable portion of the rock, occurring not only in the form 



L VI— Bull. Geol. Son. Am., Vol. 1, 1889. 



