536 GEORGE DAVIS LOUDERBACK 



border of the Myrtle areas without any evidence of contact action on 

 the practically unaltered shales; and more particularly because they 

 are apparently intruded by the dacites and andesites which are 

 abundantly represented in the Myrtle basal conglomerate and which 

 are evidently pre-Myrtle. The intrusion of the serpentines by the 

 daeitic rocks is claimed by Diller both in the Roseburg and the 

 Port Orford areas, and such observations as the writer was able to 

 make are in accord with his results. 



The absence of glaucophane and other related schists from the 

 Myrtle areas, which was stated above on the basis of field observa- 

 tions, may be theoretically correlated with the pre-Myrtle age of the 

 igneous rocks with which they are so frequently associated. 



SUMMARY 



We may conclude, then, that the time represented by the inter- 

 Dillard-Myrtle interval (perhaps including part or even all of Dillard 

 time) was a period of great igneous activity. On the other hand, 

 during Myrtle time the practically continuous sedimentation was 

 uninterrupted by volcanic eruptions, and even the inter-Myrtle- 

 Arago time interval, although representing a period of uplift and 

 considerable erosion, shows no evidence, in the areas studied, of 

 igneous activity. Vulcanism apparently lay dormant in this province 

 until the Tertiary, when, in the Arago (Eocene), the period of quies- 

 cence was terminated by the intrusion and outpouring of basalts and 

 diabases. 



ECONOMIC RELATIONS 



Purpose of the discussion. — A discussion of the economic geology of 

 this province per se would be inappropriate to the purpose of the 

 present paper, but a brief statement of the economic relations may 

 be of some value in bringing out more clearly the contrast in characters 

 between the Myrtle and the Dillard, and the difference in the geologi- 

 cal agents and processes to whose activities they have been subjected. 



THE MYRTLE GROUP 



As far as known to the writer, nothing in the way of ore deposits, 

 veins, mineralized zones, contact areas, or other like phenomena has 

 been observed in the rocks of the Myrtle group. Sedimentary 

 products of special economic value, such as coal, gypsum, iron ores, 



