44 CALIFORNIA ACADEMY OF SCIENCES. [PROC. 30 SER. 



separates into paper-like fragments, almost thin enough for 

 microscopic sections. The rock is found in two other con- 

 ditions, one opaline and the other calcareous, between 

 which and this type there are all gradations. Both these 

 less common types are hard and compact, and are quite 

 brittle, breaking with a conchoidal fracture. The opaline 

 variety has a hardness of about 5, and in places has a luster 

 like that of opal. This is No. 89, described by Dr. Hinde 

 on page 48. The calcareous rock is somewhat darker in 

 color than the others. It effervesces quite freely with strong 

 acids, while with dilute acids it behaves like dolomite. The 

 gradation of this rock into the light, earthy shale is seen by 

 testing the different specimens with acid. The different 

 grades of the rock show different degrees of effervescence, 

 while the most earthy specimens give apparently none. The 

 opaline variety does not effervesce with acid. The effer- 

 vescence is due in many of the specimens to minute cal- 

 careous remains, but in the darker rock it results from the 

 calcium-magnesium carbonate which makes up the mass of 

 the rock. All the specimens give water in the closed tube. 

 Heated they turn black, then white, giving off bituminous 

 odors. The specific gravity of the earthy specimens could 

 not be determined on account of their porous character. 

 That of the limestone is 2.69. 



No fossils of any considerable size were found in these 

 rocks. Some of the more siliceous specimens contain 

 minute, empty molds, arranged along the bedding planes. 

 In one of the more compact specimens two fragmentary 

 shell casts were seen, besides a small cast of what is prob- 

 ably Tellina congesta, Conrad. Fish-scales are quite com- 

 mon, with their delicate markings well preserved. 



Microscopic Characters. Under the microscope the shale 

 is seen to consist largely of isotropic material, in which are 

 scattered angular crystal fragments. The isotropic portions 

 of the slides appear to be, not of glass, but wholly (or nearly 

 so) of organic remains. The crystal fragments vary in amount 

 in different specimens, or even in different parts of a single 

 slide, but on the whole they form but a small percentage of 



