GEOLOGIC AGE AND GEOGRAPHIC DISTRIBUTION. 87 
clays are hard, but neither are they geologically very old, nor have 
they been subjected to that great pressure that has so often affected 
the older clay beds of the earth's crust, many of which now form 
shales and slates. 
The Tertiary geology of Arkansas south of Arkansas River has 
been described in detail by Prof. Gilbert D. Harris, a and the Ter- 
tiary and later beds of the Crowleys Ridge region of northeastern 
Arkansas by Dr. R. E. Call. 6 The present report does not under- 
take to deal with questions of stratigraphy within the Cretaceous, 
Tertiary, and Quaternary areas, except in so far as they relate to 
the details of the clay deposits. 
The general geology of the Cretaceous and Tertiary portions of 
the State should be fairly well understood by those who have to 
deal with the clays that occur in those formations. The Cretaceous 
beds are older than those of Tertiary age, which they underlie. 
They are exposed in the counties west of Arkadelphia, namely, in 
Clark, Nevada, Pike, Hempstead, Howard, Sevier, and Little River. 
Everywhere in this region they slope gently toward the southeast. 
Feet 
Fig. 5.— Section at Arkadelphia, Ark., extending from a point near the Baptist school southward to 
the Iron Mountain Railway, a, b, Sands; c, c', Arkadelphia shale; d, clay; e, gravel. 
They are made up of beds of chalk, marl, gypsum, sandstone, and 
clay. The clays of this group, however, are of comparatively small 
importance. The only extensive beds noted are the blue clays ex- 
posed near the railway in the south side of the town of Arkadel- 
phia. These clays were originally called the Arkadelphia shale by 
Prof. R. T. Hill and were believed by him to belong to the Tertiary. 
Later, however, Prof. G. D. Harris found that they belong to the 
Cretaceous. d 
It is not known that the Arkadelphia shale has any economic 
value. It is usually so interbedded with thin laminae of sand that 
it can not be used for the manufacture of pottery, but probably this 
same bed may elsewhere be suitable for the manufacture of pottery 
or available as fuller's earth. This shale bed is exposed at several 
places about the town of Arkadelphia and also on the upper part of 
Big Deciper Bluff 5 miles southwest of the town. The yellow 
sandy clay overlying the chalky marl on the Wright place, on Little 
a Ann. Rept. Geol. Survey Arkansas for 1892, vol. 2. 
b Ann. Rept. Geol. Survey Arkansas for 1889, vol. 2. 
c Ann. Rept. Geol. Survey Arkansas for 1888, vol. 2. 
d Ann. Rept. Geol. Survey Arkansas for 1892, vol. 2, pp. 15-19. 
