174 /: HARLEN BRETZ 



effect on the mass of the course of the great Vashon glacier, whose 

 volume and thickness was of course greater northward. 



Definite recessional moraines are yet unknown in the Puget 

 Soun " country. Between the terminal moraine and the southern 

 arms of the Sound are occasional moraine hills and ridges which 

 will probably resolve themselves into linear arrangement when 

 carefully studied and will constitute recessional moraine deposits. 

 But in the larger area of longitudinally ridged drift among the arms 

 of the Sound, there is little of morainic origin beyond scattered 

 lodge moraine hillocks in the valleys. 



Russell 1 first noted that there are two till sheets in Puget Sound 

 basin, recording two glaciations. Willis 2 has named these the 

 Admiralty and Vashon, with the latter of which we have had to do. 

 The frequently weathered condition of the Admiralty till or of its 

 superposed outwash has been pointed out by Willis as evidence 

 of long exposure before the Vashon glaciation. The freshness and 

 slight erosion of the Vashon till sheet and moraine evince an age 

 comparable to that of the Wisconsin drift. 



A notable feature of the Puget Sound glaciation, shown by the 

 failure of constant careful search to find older till beyond the 

 moraine, is that the last glaciation of the region, doubtless Wiscon- 

 sin in age, was the most extensive. Frequent incorporation of 

 residual soil in the Vashon till is the best evidence which might 

 be secured, in the absence of deep sections, that it overlies areas 

 never previously glaciated. 



1 Bailey Willis, "Drift Phenomena of Puget Sound," Bull. Geol. Sgc. Am., IX. 



2 Willis and Smith, "Tacoma Folio No. 54," U.S. Geol. Survey. 



