182 QUK'lvBlLVER DEPOSITS OF THE PACIFIC SLOPE. 



The dynamical action vvliicli accompanied or preceded this metamor- 

 phism was of a very violent character, so that in tlie greater proportion of 

 cases it is a manifest impossibility to construct sections of the metamorphic 

 areas, no stratum being continuous for more than a few feet. Sharp con- 

 tortion and plication are also common, but where they occur it is usually 

 apparent that the flexures have been accomplished not in the main by plas- 

 tic deformation, but by comminution of the entire mass, the residual frag- 

 ments often averaging less than a quarter of an Inch in diameter. In the 

 accompanying distortion these particles have retained approximately their 

 original I'clatlve positions and have subsequently been recemented, chiefly 

 by silica. The minute, pol^diedral rock fragments, however, have under- 

 gone no visible distortion. These occurrences coincide in a remarkable 

 manner with the results of Mr. Daubree's experiments on the frai'ture of 

 various substances by torsion and pressure.^ As is shown in Chapter III, 

 this probably indicates that, at the time of upheaval, these strata were 

 buried at a depth of not more than a few thousand feet below the surface 



Tiie most striking instances of such fracturing are met with among 

 thin-bedded rocks, either sandstones or sandy shales, and such are remark- 

 ably frequent in this series ; indeed, they might be said to be characteristic 

 of it." Thev are occasionally met with in other formations, and it would 

 be strange indeed if the conditions favorable to thin bedding had [)revailed 

 along the Coast Ranges only during a single era. As a rule, however, the 

 rocks which rest upon the metamorphic series are thick-bedded, rather coarse 

 and uniform sandstones. 



Besides this series of metamorphic rocks there are others of difTerent 

 age in the Coast Ranges to which the term metamorphic might not improp- 

 erly be applied. These will be described a little later. 



Age of the principal metamorphic rocks. With the pOSSlble eXCCptloU of the llmC- 



stone mentioned above, this metamorphic series is stratigraphically the 

 lowest in the Coast Ranges and appears to rest upon the granite. It forms 

 the crests of many mountain ranges and occupies the whole surface In some 

 of the more mountainous regions. Detailed studies of the structure show 



' Bull. Soc. gdologique France, 3il series, vol. 7, 1878-79, p. 108. 



-The peculiarity of these thin-bedded, plicated, metamorphic rocks was observed by Professor 

 Whitney. 



