Geology and Paleontology. 55° 
this is very slight, as the amount radiated per annum is only enough 
to melt 6.5 millimetres of ice.! 
Although glaciers do not conform to all the inequalities of their’ 
beds, and at the ice-falls and elsewhere became fractured, and sub- 
sequently re-united, whether by heat regulation or plastic flow, the 
fluidity theory is the most acceptable explanation of the motion of 
glaciers, even when the angle of descent is reduced to almost zero, : 
and modern observations only supplement the reasons upon which - 
Prof. Forbes proposed his theory more than forty years ago.—Prof. 
J. W. Spencer. 
A Cretaceous Brrp-Track.—Professor F. H. Snow has re- 
cently, in the Trans. Kansas Acad. Sciences, described a fossil 
bird-track discovered in the Dakota sandstone, in Ellsworth county, 
Kansas. The impression appears to have been made by the left foot 
of some bird with an elevated hind-toe just reaching the ground. 
The ball of the foot is deeply impressed and the posterior toe has 
made an unmistakable imprint, proving the avian character of the’ 
footprint. It measures two inches from anterior middle claw to 
claw of posterior toe. This discovery considerably lowers the geo- 
logical horizon of Kansas birds, since nearly all the material for 
Marsh’s Toothed Birds was obtained from the Niobrara, the highest 
group of the Cretaceous represented in Kansas. Below this lies the 
Benton, followed by the Dakota, resting unconformably on the 
Permo-Carboniferous rocks. 
Professor sSnow continues thus: “The wonderful luxuriance of 
the land vegetation of the Dakota, and its marvellous similarity to 
the Dicotyledonous forest-growths of the warm-temperate climes of. 
the present day, have rendered these sandstone beds a most fasci- 
nating field of investigation for both Paleo-botanists and Neo-' 
botanists. The finely-developed and perfectly-preserved foliage of 
oaks, willows, poplars, laurels, sarsaparillas, magnolias, sassafras and 
other kindred forms belonging to genera now long since extinct 
have hitherto suggested a beauty of landscape whose perfection was 
only marred by the apparent scarcity of animal forms. . . . . 
Our bird-track supplies the missing element of graceful serial forms. 
From the size of the footprint, it may be safely inferred that the 
bird which left it was somewhat larger than a pigeon. It was prob- 
: ly a bird with teeth,” “with habits similar to those of the modern 
ern. ; 
_ THE AFFINITIES oF Mroianta,—G. A. Boulenger reports (P 
Z. Soc. Lond., June 23, 1887) that the ‘large Plistocene Chelonian 
Miolania, which was regarded by Huxley as probably belonging to 
the group Cryptodira, and closely allied to Chelydra, Macroclem- 
mys and Platysternum, is, in fact, like all the recent tortoises of 
f ' Elie de Beaumont, Thompson Woodward and others, give range © 
rom five to eight millimetres. University of Missouri, May Ist, 1887. 
