NEOCENE STRATIGRAPHY. 309 



to simply call them the " transition beds " of the Merced 

 series, grouping them with the Merced series because 

 petrographically they are similar to the predominating 

 rocks of that series. 



THE MONTEREY SERIES. 



Lithology . — The Monterey series or formation, or, as 

 it is variously known, the White Miocene shale, or Bitu- 

 minous shale, is the most characteristic formation of the 

 Miocene. It is for the most part nearly white or light buff 

 in color, of a shaly, porous character. It is quite soft 

 and without grit, yet resisting weathering to a remarkable 

 degree, loose fragments or artificial exposures maintain- 

 ing their sharp edges. It is usually quite thin bedded, 

 the bedding being very distinct. It is generally cut up by 

 joint planes which determine the surfaces of fracture. 

 The porosity has been found in some cases to be due to 

 the leaching out of minute shells, probably foraminifera. 

 This shale has distributed through it some carbonaceous 

 material, which, though not generally showing, except 

 occasionally as small black specks, gives rise to the bitu- 

 minous springs and deposits so common along the coast. 



Near Santa Cruz, apparently underlying but probably 

 part of the same formation, is a black bituminous rock, 

 like a coarse grained sandstone, in which the matrix is 

 bitumen. Large quantities of this rock are shipped to 

 San Francisco. 



At places, as on Bald Knob near the road down Tuni- 

 tas Creek, the shale appears to be silicified into chert or 

 chalcedony or sometimes resembling opal. It maintains 

 its white color and bedding. 



At Monterey and other places it is very rich in infu- 

 sorial forms, diatoms, sponges, etc., so that it has been 

 considered as a vast deposit of such forms. Recently 

 Professor Lawson* has advanced the suggestion, upon 



*Univ. of Gal., Bull. Dep. Geol., vol. i, p. 24. 



