12 
to Peace point, and far up the valley of the Athabaska. The rivers meander 
through broad flood-plains with many islands, bars, and abandoned channels 
separated by low levees. Lake Claire basin contains wide, marshy deltas, 
formed of silt and debris brought down by Peace, Birch, and Athabaska 
rivers and divided by a complicated system of interlocking waterways. 
The only notable relief features in the lowlands are formed by granite 
hills appearing like islands in the eastern parts. These are glacially scoured 
and grooved, and contain only small patches of thin soils. 
GEOLOGY AND PHYSIOGRAPHY 
Nearly all of the surface of the park area is covered by morainic, 
fluvial, or lacustrine deposits of recent geologic time, but the position and 
nature of the underlying rocks have so influenced the development of 
present conditions that a brief discussion of them is necessary. 
The eastern boundary of the park is roughly coincident with the con- 
tact zone between the Precambrian granites and gneisses to the east, and 
the Palaeozoic sediments to the west. Outliers of the former are the 
rounded knolls rising above the delta plains of Peace and Athabaska 
rivers. The latter, sedimentary rocks, are represented along Peace and 
Slave rivers by cliffs of limestone and gypsum, which appear above Peace 
point, at La Butte, below the Government Hay Camp, and at Caribou 
island. Athabaska and Claire lakes lie in a depression crossing this con- 
tact from east to west. The inland districts show very few exposures, the 
most notable being the Salt Mountain escarpment and its northwestward 
extension, all of which is composed of Palaeozoic limestones (21). At the 
falls of the Little Buffalo there is one sheer drop of about 40 feet, with the 
lower, under-cut rock layers showing softer strata. 
The Palaeozoic sediments are very little disturbed. Extensive sink- 
hole development in the Alberta plateau district, particularly toward its 
eastern parts, is indicative of the gypsiferous nature of the underlying 
rocks (23) , and the presence of an elaborate system of underground drain- 
age. Many of the sinks have sizeable streams running into them, but have 
no outlets. Soundings made in Pine lake by the writer, resulting in a 
rough contour map of its bottom {See Figure 2), show clearly its origin 
in a series of sink-holes which have a definite alinement. Air photographs 
show that the holes have some sort of definite arrangement, the cause of 
which is not known. In some the water-level is constant, but in others 
there is evidence of very recent change too great to be caused by evapora- 
tion. In one hole along the Pine Lake-Moose Lake trail the writer 
observed shells of aquatic snails 50 to 75 feet above the present pond. 
The vegetation on the slopes indicates that the water has fallen within 
the past few years. In a small lake about 6 miles south of Moosehorn 
slough, known locally as Round lake, the water has been observed to 
change several feet in level within a year. Whether the change is a 
cyclic one and will repeat itself is unknown. There are well-defined ancient 
shore-lines on Pine lake which are at least 10 feet above the present 
water-line. 
Caribou and Birch Mountain areas are known or thought to be 
Cretaceous, and are looked upon as erosion plateaux formed through the 
long-continued dissection of the uplifted bottom of the Cretaceous sea 
