340 J. IS. Diller — Origin of Paleotrochis. 



siderable amount and yet be easily overlooked. The quartzose 

 character of the weathered matrix, however, shows that at 

 least where most coarsely granular there cannot be much if 

 any feldspar present in it. In places the matrix contains 

 numerous minute parallel scales of what appears to be sericite. 

 Associated with the most coarsely crystalline areas are a few 

 scales of brown biotite and occasionally considerable green 

 biotite, which in places is so abundant as to make quite promi- 

 nent dark green spots. Both matrix and spherulites are trav- 

 ersed in a few cases by small veins of granular quartz, showing 

 that there is a considerable amount of secondary quartz present. 

 Both spherulites and matrix are rendered slightly micropor- 

 phyritic by containing occasional crystals of plagioclase, 

 feldspar and quartz. The plagioclase, which, on account of 

 its small angle of symmetric extinction, must be an acid one, 

 in some cases forms the center from which the spherulitic 

 fibres radiate. 



An isolated specimen of Paleotrochis was cut through the 

 apices and found to be composed of granular quartz. The 

 quartz was fine-grained upon the outside where the grains were 

 set with their longest axes perpendicular to the adjoining sur- 

 face. The middle portion contained an irregular iron-stained 

 cavity possibly due to the disappearance of some iron-bearing 

 mineral. Several of the half embedded forms of Paleotrochis 

 were cut in a hand specimen to discover its relations to the 

 enclosing rock, and in each case it formed the interior portion 

 of a spherulite. Most of them contained a dark green patch. 

 The exposed conical surface of one was well striated and there 

 was an irregular depression in the apex. The form was com- 

 posed chiefly of granular quartz with a yellowish brown to 

 dark green, strongly pleochroic biotite. Near the center is a 

 small spherulite which is not only bordered by finer-grained 

 quartz but is cut by a small vein of it, showing that the depo- 

 sition of the quartz is subsequent to the development of the 

 spherulite. The embedded portion of Paleotrochis is bordered 

 by spherulitic fibers which run approximately parallel to the 

 slope of the conical surface, and it is evident that the casts of 

 these fibers produce the irregular strise or grooves upon the 

 surface of the supposed fossil. The embedded portion termi- 

 nated with an irregularly-pointed apex below. The whole 

 form is fine-grained near the border and sends small veins into 

 the adjoining spherulitic shell. These veins are so small as not 

 to be visible upon a polished surface of a hand specimen even 

 with the aid of a pocket lens, but come out distinctly in the 

 thin section. The spherulitic shell by which Paleotrochis is 

 enveloped is composed of fibers belonging to a number of 

 centers or lines and yet combined they appear to form one 



