yo H. W. FAIRBANKS — GEOLOGY OF THE COAST RANGES. 



ing very much the same lithologic character, and inasmuch as the lowest 

 Cretaceous, when it occurs, also rests unconformably on the same^eries, 

 we have the strongest evidence that this unconformity, so unequivocally 

 shown, is the same which has been found to exist in the northern part 

 of California. If it is not, then there must exist a comparatively local dis- 

 turbance and metamorphism within the Cretaceous exactly simulating 

 that at the base of the Cretaceous farther north, but the character of the 

 lowest Cretaceous found in several localities in this region utterly for- 

 bids this supposition. Let it be understood, however, that this does not 

 disprove a disturbance merely, during the Cretaceous, which the writer 

 holds is demonstrable. 



PROBABLE EPOCH OF THE SERPENTINE INTRUSION AND ITS EFFECT UPON 



THE CRETACEOUS. 



Mr Diller, in a recent publication,* says, with reference to the serpen- 

 tine, that it is undoubtedly an altered eruptive and younger than the 

 Knoxville portion of the Shasta-Chico series. With this view the writer 

 is in complete accord. Instances of contact metamorphism were given 

 in a former paper. There are no recorded observations of the serpentine 

 having been found eruptive in the Chico. About Clear lake is a large 

 area of sandstone of this age, and while serpentine occurs in the older 

 rocks near by, none is present in the Chico. It will, perhaps, be argued 

 that the Chico is generally found farther away from the axis of disturb- 

 ance than the Knoxville, which is the case along the west side of the 

 Sacramento valley ; but in several places farther south the Chico was 

 observed superimposed on the serpentine, and nowhere was it seen in- 

 truded by that eruptive. The Chico rests on serpentine in many places 

 in the Santa Lucia range, while in other localities, particularly in the 

 canyon of the Santa Ynez river, the serpentine is intruded in black shales 

 of Lower Cretaceous age. Over that great extent of country in Ventura, 

 Santa Barbara, and San Luis Obispo counties covered by the Chico- 

 Tejon there are no traces of serpentine, while in nearly every spot where 

 the pre-Cretaceous or Lower Cretaceous is exposed by erosion dikes of 

 serpentine are found. This was noted in the mountains east and north 

 of Santa Ynez, in the Santa Lucia range south of Poso, and at other 

 points farther north. 



At some period during the Cretaceous a disturbance took place, prob- 

 ably an elevation, extending through the whole length of the Coast 

 ranges, and accompanied by the extrusion of peridotitic eruptives. Al- 

 though in some cases the areas of these eruptives are very large, yet 

 the metamorphism shown by the enclosing rocks is not usually very pro- 

 nounced, while the tilting and fracturing of the strata did not extend far. 



*Bull. Geo]. Soc. Am., vol. 5, p. Ml. 



