170 The American Geologist. September, 1908. 
of debris promiscuously about the delta plain. Such inharmon- 
ious deposits may be found at any stage of the delta building. 
Other blocks of ice may have grounded and become fixed in 
the growing deposit of the delta. The resting sites of several 
presumable ice-blocks are marked by kettle-holes in the Bal- 
lardvale plain. One of good size near the northeastern margin, 
and a smaller one near the centre, are splendidly preserved and 
very typical. No drainage crease appears at the surface in con- 
nection with either of them. Probably the ice-blocks did not 
attain any great hight above the level of the delta, and the 
sub-drainage was sufficient to take care of the melting ice. 
The nature of the immediate region and the surrounding 
topography would indicate that the delta was rapidly construct- 
ed. The appearance of the esker, and "plexus" area to the 
north , the immense amount of comminuted debris , the compar- 
atively short time during which the ice-front could hold up a 
lake in this region , the assumed physical condition of the ice at 
the time, all point to a short duration for the delta construc- 
tion possibly a single season. 
The Ballardvale delta plain, though not very extensive, is 
beautifully developed, and is an admirable type of those delta 
plains formed in a temporary lake of the glacial epoch. 
AGE OF THE LAVAS OF THE PLATEAU REGION. 
By Albert B. Reagan. 
INTRODUCTION. 
1. Introduction 
2. Literature 
3. Stratigraphical Sections 
4. Stratigraphy 
5. Age of the Lavas , 
( 1 ) The Trachytes and Rhyolytes • 
(2) The Basalts 
6. Conclusion 
Within the Plateau region in the rectangle bounded by par- 
allels 32° 45' and 34° 20' and the meridians 107° 30' and 
•no° more than nine tenths of the surface is of volcanic mater- 
ial. From this main body there stretches two main arms; one 
going northwest, eighty miles to Mount Taylor, and the other 
west-northwest, one hundred and seventy-five miles, to the San 
