On the Surf ace Geology of the Basin of the Great Lakes. 213 



which assertion is supported by the fact that Sorby in England 

 has announced two new earths among the Zircons, and by tin- 

 opinion of Svanberg, who is an authority with regard to this 

 subject. 



Svanberg announced, two years ago, that the so-called Zir- 

 conia is a mixture of two different earths. 



Our investigation is merely in its beginning, and therefore 

 we can for the present only publish this short notice, but we 

 hope at a future occasion to present more definite results. 



X. — On the Surf ace Geology of the Basin <f tJu (ir.nl />Zy\, 

 and the Valley of the Mi$$ixxij>2>i. 



By J. S. Newberry. * 

 Read May 25th, 1S69. 



The area bounded on the north by the Eozoic highlands of 

 Canada, on the east by the Adirondacks and Alleghanies, and 

 on the west by the Rocky Mountains, though now, and appa- 

 rently always, drained by two systems of watercourses, may 

 be properly considered as one topographical district ; since 

 much of the water-shed which separates its two river system- 

 is of insignificant height, is composed <>f unconsolidated "Drift " 

 materials, lias shifted its position hundreds of miles, as the 

 water level in the great lakes has varied, and was for a long 

 interval submerged beneath a Mater connection uniting both 

 drainage systems in one. 



In this great hydrographic basin the Bnrface geology pre- 

 sents a series of phenomena of which the detail-, carefully 

 studied in but few localities, still offer an interesting and almost 

 inexhaustible subject of investigation, but which, a- it Beeme 

 to me, are already sufficiently well known to enable as to 

 write at least the generalities of the history which they record. 



The most important facts which the study of the ki Drift 



