100 



SCIENCE 



[Vol. LV, No. 1413 



the literature of paleontology, and it is a 

 pleasure for the writer to add a new item to 

 the information already given by Mudge and 

 Marsh, many years ago, concerning vertebrate 

 footprints of the Coal Measures of Kansas. 

 The literature has been summarized and a 

 description of a large slab of limestone from 

 Osage County, Kansas, bearing footprints has 

 been given by Moodie in his monographic work 

 on the Coal Measures Amphibia of North 

 America. No new information concerning 

 vertebrate footprints in the Coal Measui-es of 

 Kansas has been published since that work 

 appeared in 1916. The new discovery is thus 

 all the more interesting, and especially so since 

 a huge type of Coal Measures vertebrate, 

 otherwise unknown, is indicated by these 

 tracks. Moodie has likewise described, in the 

 above-mentioned work and elsewhere, skeletal 

 remains of a large labyrinthodont (?) but of 

 a size insufficient to have made the tracks de- 

 scribed herewith. 



The present discovery relates to a series of 

 eight footprints discovered by the sons of Dr. 

 George Coghill and turned over to the writer 

 for excavation and description. They were 

 discovered in a heavy sandstone, a formation 

 extending generally over eastern Kansas, ly- 

 ing just above the Weston Shales, exposed in 

 a high cliff near the Dightman bridge over 

 the Wakarusa Creek, some five miles southeast 

 of Lawrence, Kansas. The series of tracks 

 extended for a distance of twenty-five feet in 

 a direct line, but several tracks of the series 

 are evidently missing as they average about 

 two feet six inches apart, and wider spaces 

 occur in two places. 



The tracks vary slightly in size, due doubt- 

 less to the plasticity of the matrix when the 

 imprints were made. They have an average 

 of six inches in breadth, by from six to seven 

 inches in length, and both the front and the 

 hind feet appear to be represented, as two of 

 the imprints distinctly show the presence of 

 four toes, while three of them show five toes. 

 One impression seems to indicate that the 

 hind foot was placed over the impression of 

 the front foot. These footprints, if properly 

 interpreted, indicate the largest Coal Measures 

 vertebrate so far known. A more detailed ac- 



count, with photographs, will appear in a later 

 paper on the subject. 



H. T. Maetin 

 Paieontological Museum, 

 University of Kansas 



LIESEGANG RING FORMATION 



Recently, I advanced a theory to explain 

 Liesegang's rings. ^ Unaccepted theories were 

 not discussed. ^ Bradford 3 objects to my the- 

 ory, and to the omission of literature. 



That I am unaware of some work on band- 

 ed precipitates is possibly correct. However, 

 I disagi'ee with the chemical analysis * on 

 which his adsorption theory is built. I agree 

 with him that bands of lead chromate can be 

 obtained in gelatine, also with silver nitrate 

 in the gelatine and bichromate in aqueous so- 

 lution. Further, I think that banding is the 

 normal formation of precipitates, and may 

 occur in any solution. The function of the 

 gel is to fix — relatively — one of the ions, and 

 render banding visible. Ordinarily the reac- 

 tion between the ions is so violent and the field 

 of the reaction so stormy that bands are des- 

 troyed. In my theory, relatively fixed was 

 used, except in one place, and the discussion 

 shows that an absolutely fixed state was not in- 

 tended. In fact an absolutely fixed state of 

 one ion, or a relatively fixed state of both ions 

 — as in superimposed gelatine layers of AgNOg 

 and KjCr^Oj- — tends to prevent banding. Brad- 

 ford states that the ionic attraction of silver 

 and chromate is insufficient to explain banding 

 in gelatine and not in agar. However, silver 

 chromate bands form in agar quite readily, and 

 revision of the theory is unnecessary to explain 

 banding in this gel. I agree with him that 

 bands of lead chromate can be obtained in gela^ 

 tine with proper concentrations of lead acetate 

 and potassium bichromate. Direct reversal of 

 the solutions, however, without change of con- 

 centrations is not a reliable method. 



Band formation is beautifully illustrated ia 

 the growth rings of trees. Rings in gels are 

 formed similarly. 



1 Science, July 22, 1921. 



2 Bancroft, "Applied Colloid Chemistry," 1921, 

 p. 259. 



3 Science, Nov. 11, 1921, p. 463. 



4 Biochemical Journal, 1916, X, p. 173. 



