﻿ASRESTOS AND MANGANESE DEPOSITS. 155 



JIETAMORI'IIISM. 



The evidence is plentiful of there having been considerable dynamic 

 metamorphism in former times in this region. It is not local, but 

 regional, for there are very few parts of the Archipelago which do not 

 exhibit it. In the Ilocos country the metamorphism can be considered 

 under two heads, as follows: 



Serpentinization — dominated by chemical alteration. 



Formation of schists — dominated by physical re-formation. 



I have not yet seen any evidence of there being contact metamorphism, 

 although I expect it to be discovered after further search, and then 

 somewhere along the border of the granite (f. n.). 



Serjjentinization is by far the most important from an economic stand- 

 point, and therefore it will first be considered. Nearly every hand 

 specimen of the basal rock in the district shows some alteration, and this 

 alteration is usually to serpentine. The asbestos deposits occur in veins 

 and pockets in the fractured serpentine masses. This serpentinization 

 is quite common in Philippine basic rocks ; I have seen it on Batan Island, 

 and along portions of the Zambales coast. Mr. Becker also cites several 

 other localities. In Ilocos Norte it is more pronounced on the Dungn- 

 Dungon estate on the Baruyen River. At Dalumat, near Pasuquin and 

 in fact wherever the pyroxenite mass in exposed, some degree of serpen- 

 tinization will be seen. ' In all the slides so far examined from this region 

 the alteration has been from rhombic pyroxenes. (See PI. VII, fig. 7.) 

 I have noted the alteration from olivine in other parts of the Islands 

 but not here. 



The pseudo-conglomerate in the serpentine. — Very characteristic fea- 

 tures of the serpentine formation are in the brecciation and the con- 

 glomeratic appearance in many localities. I have called this type of rock 

 a pseudo-conglomerate. This broken and bowldery condition is quite 

 marked and is confined largely to the borders of the mass, along or near 

 the schist zone. Some of the fragments are small, angular blocks ; others, 

 immense rounded bowlders. "Slickensides" is a very characteristic fea- 

 ture in this part of the formation, and the brecciation in this and the 

 jasper formation afford ample proof of the tremendous dynamic move- 

 ments in this region. That these dynamic forces are still at work is 

 quite probable, as Luzon is subject to frequent earthquakes, although it is 

 true that this part of the island is less liable to have them occur than the 

 regions farther south. The photograph (PL V, fig. 8) is of this pseudo- 

 conglomerate near the Baruyen River at Baruyen Hill. 



The schists. — Schistose rocks are apparently scattered quite generally 

 throughout the length of Luzon, as well as in the other islands of the 

 group ; naturally, they are confined to the mountainous portions where 

 there has been a considerable amount of dynamic movement. In Ilocos 



