THE LOUP FORK GROUP OF KANSAS. ■ 207 



twenty specimens representing different stages of growth; some quite small, show- 

 ing the elegant markings of the shells, ridges and grooves following the outlines 

 of the plastron plates. Some specimens were nearly perfect, lacking, however, 

 the skull. A number of nearly perfect limbs and arches were obtained. They 

 were found in a narrow gulch where the water had cut through twelve or fifteen 

 feet of white sandy marl. The specimens were sticking out on either side of the 

 perpendicular banks. During October, at the Museum of Comparative Zoology, 

 Cambridge, I was able to get some of the specimens into very respectable shape, 

 though the specimens have still fragments with them, and it requires time and 

 patience to fully restore them. I believe they have been described by Prof. 

 Cope under the name of Xerobates cyclopogius. They are but little petrified, 

 which is the case with all the Loup Fork fossils. I have always found that fos- 

 sils partake largely of the characters of the rocks in which they are preserved. 

 If it is hard and dry the specimens are well preserved and the breaks are usually 

 angular and rarely mended. Specimens are generally well preserved in loose, 

 dry sand, in chalk, and in hard clay concretions. The older the formation the 

 more perfect is the petrifaction. In some cases the bone is entirely replaced by 

 silica. Where the matrix is largely composed of clay it cracks and crumbles on 

 exposure to the atmosphere and it is very difficult to save the specimens unless 

 they are preserved in concretions impregnated with iron. In recent formations, 

 unless the bones are perfectly dry, they usually crumble easily, and it is hard to 

 mend the fragments, the cement used is apt to tear loose and take part of the 

 bone (especially spongy bone) with it. Further, if any fragments have been left 

 in the field the difficulties of restoring the specimen are greatly augmented. 



One trouble the explorer meets with in northwestern Kansas is from the fact 

 that so few fossil beds are exposed, the slopes of the hills are so gradual that the 

 greater part of the country is covered with grass and soil. The south sides of 

 streams are the ones usually denuded. I suppose this is because the streams, 

 flowing as they do in a northeasterly direction, cut the southern sides, and in ad- 

 dition the higher bluffs protect that side from the south wind and the sun so that 

 snow and moisture remain there longer, giving Jack Frost a chance to break off 

 great masses of rock which, rolling down the bluffs, cover their sides and prevent 

 the growth of grass to some extent. On the southern sides of the Sappa and 

 Beaver Creek are often seen bluffs a hundred feet or more- in 'height with bold 

 escarpments rising one above the other, while between them are beds slanting 

 backward of the soft fossiliferous marls. Where the marls are perpendicular caves 

 are often cut in them by rain finding a crevice in the hard cap above, to rush 

 through and wash away the softer rock. 



In one of these caves Mr. Wright of my party found where an Indian had 

 been buried and took away a few glass beads. He found it rather dangerous 

 work getting down from the over-hanging rocks into the mouth of the cave and 

 still harder to get back again. I believe I may take to myself the credit of being 

 the first to explore these beds in northwest Kansas. For, though collections of 

 mammalian bones had been found by Profs. Marsh, Mudge and others in the con- 



