308 
MAZATZAL QUARTZITE 
croaching sea. Of course, such a delta must have been very large 
in order to answer the requirements of the area of the Mazatzal 
quartzite; but the delta of the present-day Ganges River for in¬ 
stance, has a front of about 220 miles, an inland extension of 
about 200 miles, and a tidal range of about 16 feet. 
The observations made regarding the probable nature of the old 
surface upon which the Mazatzal sands were deposited suggest a 
gently undulating plane that consisted mainly of schists and 
granites containing occasional quartz-veins and minor intrusives. 
It is not within the scope of this article to include the consideration 
of the schists, granites, and similar rocks of Pre-Cambrian date; 
but it may be said in passing that the presence of a considerable 
thickness of quartzites and slates within the schist massif of the 
North Peak section of the Mazatzal Mountains, indicates the 
existence of a cycle of events earlier than, but similar to, those 
which obtained during the .deposition of the quartzites especially 
studied. 
As already stated, the basal conglomerate of the great quartzite 
sequence is in some places entirely absent, but in the Tonto Creek 
area it is well presented, and in the Natural Bridge section it 
attains a thickness of often 300 feet. The old land-mass may 
easily have possessed local valleys, or basins, which, after sub¬ 
mergence, would naturally catch the coarser material beaten down 
from the cliffs or reworked from a young delta. This would ex¬ 
plain the presence of the coarse arkosic material, together with the 
pebbles of both subangular and ovally-rounded character. Where 
such depressions in the surface did not occur, the quartzite series 
might naturally enough begin abruptly with its fine materials 
resting directly on the older rocks, as obtains in the North Peak 
section. 
The whole succession above the basal conglomerate, is charac¬ 
terized by being almost consistently irregular; namely, fine-grain¬ 
ed, cross-bedded material suddenly becomes coarse and then fine 
again; then there is a lense, or a bed of ripple-marked, sun- 
cracked, red shale or slate, that often contains sand; then fine¬ 
grained material again, and so on. This, if we follow Barrell, 
approaches closely the texture to be expected in delta deposits. 
The shale, or slate, beds, always lenticular in cross-section, would 
