THE DEEKFIELD SHEET. 435 



The diopside is iu stout, small ciystals or in long, stout prisms, some- 

 times broken. They are enveloped by the aeguiue-augite without common 

 orientation. 



AMYGDALOIDAL SANDSTONE. 



One of the columns of sand rising from the sandstone and penetrating 

 the basal bed at the Greenfield quan-y expands 9 feet from the base, where 

 it passes above the basal bed into the glass-breccia, and its central jjortion 

 presents a scoriaceous appearance. It is a red sandstone filled with more or 

 less rounded spots of a white silicate, which I have no doubt, from my 

 examination of other similar cases, is mainly a granular plagioclase. The 

 same thing is developed much more extensively at the top of the breccia, 

 on the path going up over the cliff north of the quarry. Here for several 

 feet in thickness the rock is a red sandstone closely filled with small cavi- 

 ties. The whole makes the impression of a rather coarse, red amygdaloid 

 with white amygdules. 



A still more attractive form of the same rock is found in the cut of 

 the electric road at the Deei-field River, a mile south of Cheapside (see 

 PI. VIIIc, fig. 3). Here a light-red sand rock is filled with the fresh white 

 amygdules. Under the microscope the sandstone between the white fillings 

 has a beautiful fluidal structm-e, thus heightening the resemblance to an 

 amygdaloid. The cavities are superficially blackened by the recrystalliza- 

 tion of the iron oxide. The white filling is mainly a fresh matted network 

 of plagioclase blades, which shows distinct triclinic striation rather more 

 frequently than is usual in this water-deposited feldspar. They are ragged- 

 edged from interference due to rapid crystallization. In the center of the 

 cavities is another mineral into which the feldspars penetrate with a micro- 

 pegmatitic structure or which runs out among them. It polarizes with 

 bright yellows, and I suspect it to be datolite, as a mineral with the high 

 glassy luster of datolite can be seen with the lens in the centers of some 

 cavities. It shows no cleavage, and it has a rough surftice like olivine, 

 which agrees with the high refractive index of datolite. Other slides of 

 this occuiTence showed a curious radiate-fibrous structure with coarsely 

 beaded fibers and extinction up to 40°, and some smaller stout, square 

 prisms with flat ends. They present all the peculiarities of wollastonite. 

 Another peculiarity is that the cavities seem to have been filled with the 

 mixture described above, after which the sand has shrunk away from the 



