224 Pwm/pelly and Van Hise — Observations upon 



Art. XXYII. — Observations upon the Structural Relations 

 of the Upper Huronian, Loioer Huronian and Basement 

 Complex on the north shore of Lake Huron ; by Raphael 

 Pumpelly and C. R. Van Hise. 



During- the past summer we visited the north shore of 

 Lake Huron in order to find evidence, first, as to whether the 

 Original Huronian of Logan and Murray is divisible into two 

 series as recently advocated by the late Professor Alexander 

 Winchell ; and, second, to ascertain more definitely the rela- 

 tions which obtain between the Lower Huronian and the Base- 

 ment Complex of the region, usually called Laurentian. The 

 term Basement Complex is here preferred in order to avoid a 

 discussion as to any correlation with the original Laurentian 

 rocks. 



Helations of the Upper and Lower Huronian. 



Prof. Winchell found, as he thought, evidence of two series 

 in the Original Huronian near Echo Lake. At this place, 

 according to him, there is in descending order, a slate-conglom- 

 erate and quartzite with a clip of about 20°. There is then an 

 interval of a third of a mile, after which appears a quartzose 

 slate-conglomerate, followed by quartzite, and this by alterna- 

 tions of quartzite, quartz-schist, and various slates, schists ■ and 

 argillites, the series having a dip of 75° to 80° southwesterly, 

 and being as a whole more crystalline than the first slate-con- 

 glomerate and quartzite. A break is consequently placed 

 hetween the two, the upper series including all of the lime- 

 stones and intervening formations of Logan and Murray's 

 Huronian.* 



About two miles east of Garden River is a ridge of banded 

 blue and cream colored limestone fully 200 feet high, which 

 may be easily found as a quarry is here located. Its strike is 

 about ]ST. 30° W., and its dip 45° south of west. On its steep 

 northern slope, and underlying the limestone, is found the 

 typical lower slate-conglomerate. The actual contact between 

 the two was not found, although they are separated by only 

 about 50 feet at one place. The lowest layer of limestone is 

 very siliceous, probably indicating that the passage from the 

 conglomerate to the limestone is a gradation such as ordinarily 

 occurs when a change takes place from mechanical to chemical 

 or organic sedimentation. The exposure of lower slate-con- 



* A Last Word with the Huronian; Alex. Winchell: Bull. Geol. Soc. America, 

 vol. ii, pp. 114-124. 



