June, 1906. New Forms of Concretions — Nichols. 33 



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 90 . There 

 was a third cleavage parallel or nearly so, with the plane of the slide 



