196 The Development Theory.. 



glacier that brought its heavy boulder masses 

 to their present place, the history of the occa- 

 sional piece of granite that seems so far out 

 of place among porphyries and basalts as to 

 suggest an iceberg journey from some north- 

 ern shore, all these fragments of story un- 

 avoidably come into our conception of the 

 creation of the boulder drift that constitutes 

 the second layer of our Portland mountain. 

 Then we shall find ourselves in the presence of 

 the basaltic layers of what were once, without 

 doubt, great lava flows over level causeways 

 long since eroded by deep valleys or narrow 

 ravines until the direction of their outflow 

 seems now almost incredible. 



We now reach the basement sedimentary 

 rock upon which all this upbuilding has been 

 erected. You will find it in a few places crop- 

 ping out in the river bank at low water. It 

 extends back under the mountain to Tualatin 

 plains; it forms the foothills around the plains; 

 it borders the valley, forming its foothills 

 through South Tualatin, Wapato lake, Amity, 

 Albany, Eugene, and back down the valley 



