70 HAROLD W. FAIRBANKS 



angular fragments are not due to atmospheric agencies alone, 

 but that they are capable of being produced in thick-bedded 

 rocks as well as in thin-bedded which have not been greatly 

 sheared, but subjected to a rending strain. Such rocks under 

 proper conditions can become recemented and apparently as 

 massive as before. The cracks may thus become completely 

 closed, or left slightly open and filled with calcite or quartz. 

 Subjected to atmospheric agencies lines of weakness are soon 

 developed, and the rock crumbles in angular pieces. A similar 

 rock which has not undergone this breaking strain will weather 

 either in large rounded knobs, or, if it be soft and argillaceous, 

 break up into fragments more or less conchoidal. 



Professor Lawson remarks further upon this subject as fol- 

 lows : "The superficial study of this phenomenon has led to 

 grossly exaggerated views as to the amount of disturbance 

 (shattering) to which the Coast Ranges have been subjected. 

 The sharply marked alternation of wet and dry seasons, com- 

 bined with the treeless character of many of the ranges, is 

 peculiarly favorable t) this disintegration." 



It is only necessary to compare the most of the sandstones 

 of the Golden Gate series with those of the Cretaceous or Ter- 

 tiary to see the vast difference in the manner of weathering. 

 As a result of my experience through nearly the whole of the 

 Coast Ranges, I feel satisfied that peculiarities of climate have not 

 been the cause of the phenomenon under discussion. The abun- 

 dance of cracks and shear planes in the older rocks is one of the 

 chief reasons why it is so difificult to obtain good building stone 

 from them, although the sandstones are characteristically thick 

 bedded. 



I think that Professor Lawson has underestimated the 

 amount of disturbance to which the Golden Gate series has been 

 subjected. It is not necessary for the folds to be involved or 

 intricate, although they certainly are in many places, for it to 

 have undergone a large amount of strain, fracturing, and shear- 

 ing. 



Professor Lawson professes to be entirely ignorant of the 



