648 > / HARLEN BRETZ 



glaciation should be either lowan or Illinoisan in age. Farther than 

 this, the writer does not care to go. Ordinary criteria in use east 

 of the Rocky Mountains for differentiation of drift sheets cannot 

 safely be used for the correlation of these glaciations in Washington. 

 The only one relied on here is the moraine-building habit of the 

 Wisconsin ice sheet, a character which seems to have been world- 

 wide.^ 



There were no channeled scablands on the Columbia Plateau 

 before the Spokane glaciation. A mantle of loess, with a mature 

 topography, completely covered it. The evidence for this con- 

 clusion is found in the great and remarkably persistent width of the 

 Cheney-Hooper scabland tract throughout a length of 70 miles, and 

 the various distributary courses out of it, some of which never were 

 eroded to the basalt. These features never could have been formed, 

 had spillways like those of the present existed. But with early 

 escape southward retarded by the loessial hills and their small 

 drainage ways, a wide spreading among them necessarily occurred, 

 and some distributaries were able to cross to Crab Creek drainage. 



A puzzling situation regarding glacial drainage exists in the 

 vicinity of the small Spangle lobe. There is no adequate drainage 

 route around it for glacial waters which came from Idaho and 

 western Montana and entered the Cheney-Hooper scabland tract. 

 Two spillways exist north of Mica, between Lake Spokane^ east of. 

 this lobe and Pine Creek channel. Both have erratics in them, the 

 highest at 2,550 feet A.T., but neither carried much water. There 

 is no error involved in mapping this lobe because an ice dam at 

 Spangle is required for the operation of the Pine Creek channel. 

 This channel carried far more water than the Mica spillways, 

 water derived directly from the Spangle lobe. Yet it also is inade- 

 quate for the drainage in question. And much more water went 

 down the Cheney-Hooper scabland tract, in proportion to the 

 immediately tributary ice edge, than passed through any other 



'^ No till or other evidence of pre-Spokane glaciations has been found beneath the 

 loess (save only the Cheney deposit). No till has been found in the scablands. The 

 writer is unable to agree with J. T. Pardee who states {Science, Vol. LVI [December 15, 

 1922], pp. 680-87) that till occurs at "scores" of places on the plateau south of the 

 limit of Spokane glaciation, as mapped in Plate III. 



2 Thomas Large, Science, Vol. LVI (September 22, 1922), pp. 335-36. 



