Hawortu. | Physical Properties of the Tertiary. 257 
stance. When examined with polarized light it is almost entirely 
free from double refraction, in which respect it further resembles 
elass.. The color of this material is variable passing from almost a 
pure white to various shades of light buff. It is frequently well 
stratified, sometimes even to minute proportions. ‘The lesser strati- 
fication surfaces occasionally have most delicate and beautiful wave 
lines marked in them, such as might be produced by gentle wave 
action in water or wind action upon a dry surface of the material. 
Plate X X XIX represents the ash as it appears well stratified along 
the south bank of a tributary to Spring creek about a mile west of 
Meade. The upper layer, 4 feet thick or more, is very weakly 
cemented, yet it has more firmness than the lower beds which are 
eradually blown away by the winds leaving a slight projection of the 
upper and heavier beds. The lower beds gradually disappear to the 
right, near where the man is standing, and have their stratification 
lines converging in that direction as is faintly shown in the plate. 
Elsewhere the ash rarely if ever shows such prominent stratification 
lines. 
The localities at which this volcanic ash is found are relatively 
numerous, but seem to be entirely disconnected. What seems to 
be the same material is found in different places in Nebraska, in a 
dozen or more counties in western Kansas, and westward into Colo- 
rado. Sometimes it covers but a few square rods in area, and rarely 
more than a few acres. Cragin! has suggested that these isolated 
deposits be considered as a definite terrane and has offered the name 
Pearlette Ash for it, the name referring to an abandoned country post- 
office on the plains of Meade county. There is no evidence of any 
relation between the different isolated deposits excepting as it seems 
probable to some that they must have been formed at about the 
same time on account of their probable origin as implied by the 
name voleanic ash. As itis yet an open question regarding the true 
nature of the material, and much more so regarding its mode of 
deposition, it is hardly desirable to draw many conclusions from 
their supposed origin. It is correspondingly less desirable to group 
the little isolated patches together and assign them to a geologic 
terrane including nothing else. 
1 Prof. F. W. Cragin, The Pearlette Ash; Colorado College Studies, Vol. VI, p. 54, 
Colorado Springs, March 1896. 
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