SCIENCE. 
404 
Undulations in clay deposits. 
A ditch about two feet deep, and running nearly 
east and west, on the grounds of this college, presents 
a profile as if the clay (which is of unknown depth) 
had been shaped into undulations, with crests from 
eight to fifteen feet apart, and then covered uncon- 
formably by the sandy soil, which over the crests is 
about two or three inches deep, and in the troughs 
about two feet at most. The ‘strike’ of the crests is 
nearly north and south. This peculiar formation has 
been observed over a large area of country in this vi- 
cinity. A surface peculiarity is the occurrence, at in- 
tervals of one or two hundred yards on the prairies, 
of low mounds a foot or two high, usually covered 
with dewberry briers. West of this place, in Milam 
and Williamson counties, the nearly level prairies are 
mammillary, with slight elevations eight or ten feet 
apart, presenting the appearance of old tobacco or 
potato hills on a gigantic scale. These appearances, 
visible from the cars, excite the curiosity of all who 
observe them; and a plausible theory of their cause 
might not only gratify this, but lead to some very 
important discoveries in dynamical geology. For 
these reasons I desire to present this problem to 
your geological readers; and, if it has already been 
solved, my apology for ignorance of the solution must 
be that I am not a geologist. foe sD) 
Agricultural and mechanical college of Texas, 
College Station. 
‘A singular optical phenomenon.’ 
Having made the phenomena of binocular vision a 
special study for many years, I was greatly interested 
in the letter of ‘F. J. 8.’ in Science, No. 57. Bugee 
confess I do not quite understand it. I can but 
think that the phenomenon he describes is only an 
example of ‘phantom image,’ produced by binocular 
combination of similar figures of a regular patterned 
field — in this case, the squares of the coarse screen. 
But in that case the image ought not to be inverted 
nor enlarged. As to the inversion: if, as I suppose, 
your correspondent imagines it inverted only because 
it moves with the head, he is probably mistaken. 
There is no optical law by which an inverted image 
could be formed under the conditions described. ‘The 
movement of the image is simple parallactic motion. 
The point of sight being the centre of parallactic 
rotation, if the image be nearer than the object, the 
motion will be in the same direction as that of the 
head of the observer; but, if the image be farther off 
than the object (a far more difficult case), the motion 
of the image will be opposite that of the head. 
There still remains, however, the enlargement of 
the image. Thisis incomprehensible tome. It ought 
to be diminished in exact proportion to its nearer 
distance. Neither can I at all understand what is 
said about the phenomenon as seen by a near-sighted 
person. I should be glad if your correspondent would 
repeat and describe more accurately the phenomenon; 
for there are no phenomena more illusive, and requir- 
ing more practice to understand, than those of bi- 
nocular vision. If I am right as to the nature of the 
image, it ought not to be seen with one eye only. 
The subject of phantom images is fully explained 
in my little volume on ‘ Sight,’ pp. 107-119. 
JOSEPH LECONTE. 
Berkeley, Cal., March 18, 1884. 
The possible origin of some osar. 
The writer does not profess to have an extensive 
acquaintance with these problematic structures; but, 
(Vor. IIL, 
a few examples having been discovered in his re- — 
searches in Dakota, the subject of their origin was 
been thrust upon him. 
From several considerations, which need not be 
given here, it seems extremely improbable that the 
quaternary glaciers in that region bore, either on their 
surface or in their depths, any considerable amount 
of débris, at least nothing coarser than dust upon 
their surface, and perhaps gravel in their lower por- 
tions. How, then, can steep meandering ridges nearly 
continuous for miles, ten to thirty feet in height, run- 
ning nearly at right angles with a great moraine, and 
much more stony than the surrounding surface and 
the general mass of the till, be explained ? 
The following hypothesis is offered for criticism. 
Given a sub-glacial stream, or a super-glacial one, 
which, near the edge of the ice-sheet, has cut an ice- 
cafion through to the ground moraine: the presence of 
the ice-cliffs on either side would tend to force a plas- 
tic body like the till toward the stream, and cause it 
to rise underneath the stream, like the ‘ creeps’ fre- 
quently occurring in coal-mines or deep cafions. Now, 
if the streams have only a velocity sufficient to wash 
out and carry off the finer material, the bowlders and 
gravel will be left in excess, and in ridges along the 
line of the stream. Of course, stratified beds of sand 
and gravel would form a considerable portion of hills 
produced in this way, just as in the case of those 
formed according to the usually accepted theories. 
Similar breaks and lateral repetitions of the ridges 
might result according to either of the theories. 
It seems, moreover, not improbable that some of the 
re-entrant spurs of terminal moraines may have begun 
in this way; the cafion developing into a notch, and 
giving rise to lateral flowage of the ice, as well as in- 
creeping of the till. J. E. Topp. 
Tabor, Io. = 
Osteology of the cormorant. 
In late numbers of Science, several communications 
have appeared from Dr. Shufeldt (ii. 640, 8225 iii. 
148) and Mr. Jeffries (ii. 789; iii. 59) on the ‘ oste-, 
ology of the cormorant,’ and especially on so-called 
‘occipital style;’ and complaint is made by Mr. Jef- 
fries (iii. 59) that Dr. Shufeldt ‘does not mention the 
nature of the bone’ in question. Neither gentleman 
seems to have been thoroughly acquainted with the 
literature of the subject; and inasmuch as both are 
members of a committee of the American ornitholo- 
gists’ union, appointed to investigate the anatomy 
and physiology of the birds, they may be thankful 
for a reference to a special paper on the anatomy and 
functions of the bone in dispute. It is to a memoir 
by William Yarrell that I refer. Yarrell designated 
the ‘ occipital style’ of Shufeldt as the ° xiphoid bone,’: 
and in 1828 communicated to The zoological journal 
an article (iv. 234-237, art. xxviii.) ‘on the use of. 
the xiphoid bone and its muscles in the corvorant 
(Pelecanus carbo Linn.),’ which is accompanied by 
two figures on plate vii. (figs. 5 and 6) illustrating the 
skull, with the xiphoid bone, and the muscles in © 
relation with it and the lower jaw. The development 
of the peculiar bone is correlated with the weakness 
of the lower jaw; but for further information those 
interested must refer to The zoological journal, where. 
they will likewise find references to the views of 
other authors. . 
Lest Science or myself should be charged with — 
making or overlooking a typographical error, I beg 
to add that ‘corvorant’ is the substitute for cormo-- 
rant, adopted by Yarrell, probably from a false or 
confused idea as to the etymology and history of the 
word. THEO. GILL. - 
