106 Tfie American Geologist. Feb. isoo. 
slightly tip, so that an immense ])rcssnre was brought to bear 
on the small surface, causing the formation of a gouge- 
like crescentic hollow, with the concavity towards the origin 
of the motion, i.e., facing up the valley. 
In making my first explanation I wrongly inferred that 
there might be an "advancing and receding motion of the gla- 
cier," so as to cause the stone to turn over. 
In some way, then, due both to the striking or pushing force 
of the glacier, and to the local pressure resulting from the pres- 
ence of a boulder between the ice and the rock surface, the 
boulder was not as with the rest of the ground-moraine push- 
ed gradually and slowly onward, but hitched, thus causing it 
to break off the lunoid fragment on a surface peculiarly liable, 
under great local pressure, to exfoliate. 
Prof. Chamberlin remarks that he has not seen any "lun- 
oid furrows." What,however,we call lunoid furrows are apparent- 
ly identical with his "crescentic gouges" or "disruptive gouges" 
such as are represented by his fig. 34. In fact my photograph 
of the glacier garden at Lucerne, with the crescentic gouges is' 
almost identical in appearance with his fig. 74. 
EDITORIAL COMMENT. 
THE AZOIC SYSTEM. 
The following is quoted from the new Century dictionary : 
The "Azoic system" or series of Foster and Whitney includes the 
stratified rocks, together with the associated unstratified ones which 
underhe unconformablj^ or are otherwise shown to be older than the 
Potsdam sandstone, or the lowest group of rocks which has up to the 
present time been proved to contain traces of a former organic life. 
The following is quoted from Foster and Whitney's report 
on the lake Superior land district, 1851, Part ii, p. 3 : 
Below all the fossiliferous groups of this region tliere is a class of 
rocks, consisting of various crystalline schists, beds of quartz, and 
saccharoidal marble, more or less metamorphosed, which we denom- 
inate the Azoic SYSTEM. This term was first applied by Murchison 
and Verneuil to designate those crvstalline masses which preceded the 
paleozoic strata. In it they include not only gnei'-s, but the granitic 
and Plutonic rocks by which it lias been invaded. "We adopt the term, 
but limit its signification to those rocks which are detrittil in their 
origin, and were supposed to have l)een formed before the dawn of 
organized existence. 
The definition from the dictionary is seriously defective. It 
will be noticed that it includes the unstratified rocks, in the 
