Methods of Stratigraphy.— WincheU. 345 
Azoic Group of Norway," and greatly anterior to the Cam- 
brian. 
The idea Dr. Bigsby entertained of the Huronian, while 
professedly based on the original descriptions of Logan and 
Murray, is widely variant from them. He referred to, and 
used such parts of their descriptions as suited his purpose, 
but derived (more largely probably from his own observations 
about the Lake of the Woods) a "Huronian" that agreed more 
nearly with that system of rocks which has more recently been 
designated Keeioatln, a series of greenish schists, greenstones 
and gray-wackes, with some argillytes and agglomerates. 
With that facility which has at various times marked the 
versatile perceptions of Dr. T. Sterry Hunt, this idea was at 
once accepted by him, and urged as the correct expression of 
the Huronian system,* and it is probakly due largely to his 
writings that the"greenstone"idea of the Huronian was widely 
received and accepted favorably by geologists in North Amer- 
ica. 
Still a different idea is at present entertained by the 
otiicers of the Canadian Geological Survey. Perceiv- 
ing the necessity of admitting into the Huronian the 
non-crystalline strata described on the north shore of 
lake Huron, and repeated in 1863 by Sir Wm. Logan 
in the "Geology of Canada," they are forced to extend 
the Huronian system from the bottom of the Silurian 
wherever that may be, or at least from the bottom of the 
Cambrian, wherever that may be, and if it exist at all in North 
America, downward to the "Laurentian," wherever that may 
be. This makes it include not only the original Huronian. 
and the "greenstone" idea of Bigsby and Hunt, (the Urschiefer 
of Norway) but also the true "crystalline schists" of a still 
lower horizon, and so amplifies the term that it well nigh falls 
to the ground from the burden of its own weight.* It should 
be admitted that the extension of the term downward so as to 
include strata not embraced in the descriptions and sec- 
tions published by Logan and Murray (1848-1863) may be to 
some degree justified by the mapjnng of the Huronian which 
^Geognosy of the Appalacliians. A.A.A.S. vol. xx. 1871; Chem. 
and Geol. Essays, p. 269. 
'Trans. Roy. Soc. Canada, vol. vi. Sec. iv. p. 3. 18S8. Presiden- 
tial address of Dr. Robert Bell. 
