JUNE, 1906. NEw Forms or CoNCRETIONS—NICHOLS. a8 
trate. While the projecting and visible portions are plane, that 
portion of each plate which is buried in the mass of the aggregate is 
invariably curved and frequently very strongly so. Hence a plate 
that appears from the general form to pass through the basal plate 
frequently curves sharply into almost a U shape, with both sides 
projecting upon the same side of the specimen while another similar 
U-shaped plate lies symmetrically in the opposite rosette. Other 
plates upon approaching plates that they appear to penetrate, termi- 
nate there in a wedge, and a similar form symmetrically placed gives 
the appearance of a penetration that does not exist. In some in- 
stances the aggregations are double. One specimen consists of two 
rosettes in parallel position which have simply touched each other 
and adhered. Another consists of two individuals at right angles 
which have grown together giving the effect of a more or less spiral, 
elongated form. | 
The exterior of the specimens is of dark reddish-brown color, 
while the interior is of a pale pink closely resembling the color of some 
pink orthoclases. When broken a good cleavage developes in the 
form of a minute step structure of very brilliant facets in parallel 
position with pronounced pearly lustre. When the fracture is ex- 
amined under the magnifying glass the cleavage is obscured by a 
granular structure which is exactly that of a broken face of sand 
stone. The specimen is obviously composed of grains of sand ce- 
mented by a mineral which possesses an eminent cleavage in at least 
two directions. The average specific gravity of the nodules is 3.348. 
The individuals do not vary greatly in density from this mean. The 
color is discharged upon intense ignition but returns upon cooling. 
The color after ignition however, is fainter than before. 
A slide was prepared and studied under the microscope. This 
appeared as an aggregate of angular quartz fragments of several sizes _ 
enclosed by a cementing mineral which completely filled all voids or 
interspaces between the quartz. The quartz grains were surrounded 
by a thin red coating which resolved under high power into groups of 
brownish-red isotropic spherules and ellipsoids upon the surface and 
in the fractures of the quartz grains. The granular fragmental 
material was almost wholly quartz. One small, isotropic fragment 
of yellow color, high refraction and no visible cleavage, presumably 
garnet and one good sized fragment of clouded orthoclase appeared. 
The cement was an anisotropic mineral of two cleavages, one 
better defined than the other, which lie at an angle of go°. There 
was a third cleavage parallel or nearly so, with the plane of the slide 
