8 



University of California. 



[Vol. i. 



except for particular layers unusually rich in infusorial forms. This 

 idea, if sustained, of the volcanic origin of the Monterey series is of 

 much interest, since the series has a constant general character 

 for several hundred miles along the coast and the rocks composing 

 it are probably made up of the same materials. 



The Monterey series is over one thousand feet thick in the dis- 

 trict around Carmelo Bay, and the whole series has been thrown 

 into undulatory folds, the dip not exceeding usually io° to 20 . 



Since their deposition the rocks of Monterey series have been 

 subjected to uplift, the minimum value of which is locally not 

 less than one thousand feet, and the Carmelo Valley, with a width 

 on its bottom of half a mile, has been worn out to base level 

 through them. 



Within the area examined are six geographically distinct patches 

 of volcanic rock which a*©- of peculiar mineralogical composition 

 and for which the name Carmcloite is proposed. Some specimens 

 yield to chemical analysis results which ally them with the basalts, 

 while others correspond rather to the andesites. These eruptive 

 rocks, though varying much in aspect, texture, structure, and com- 

 position, are probably derived from one magma, and are of the same 

 age. They are characterized by the presence of an interesting 

 mineral, here named iddingsite, of which a detailed description is 

 given in the sequel. The areas occupied by these rocks are sepa- 

 rated by reason of their being mantled by later formations, and their 

 outcrops are simply their protrusions through the overlying and 

 newer rocks. If the latter were stripped off, the six separate patches 

 would probably fall into three, and possibly only two, distinct areas. 

 These eruptive rocks are certainly of later age than both the 

 Carmelo series (Eocene) and the Monterey series (Miocene). They 

 belong to the age of the terrace formations referred to below. They 

 are submarine extravasations intercalated with the Pliocene f?) forma- 

 tions. 



Imposed upon the worn slopes of the rocks of the Monterey 

 series (Miocene) are various formations of conglomerate, sandstone, 

 gravel, sand, and clay. As indicated by their petrographical desig- 

 nations these formations are in some places quite coherent and 

 firmly cemented, while at others they are loose and incoherent. The 



