NORTH AMERICA AND THEIR VERTEBRATE FAUNA. 21 



"The red shale is in many cases somewhat obscurely stratified, showing hardly 

 any lamination or other perceptible structure in beds several feet thick. In places 

 where it is mingled with gray or white layers, the stratification is very trenchantly 

 shown. In some such exposures contemporaneous unconformities are to be seen, 

 where a series of overlying laminated shales bend in conformity to the surface of a 

 local excavation in an underlying horizontally stratified clay or shale. 

 Concretions in the Shale. 



"The red shale usually contains numerous concretions of material which once 

 no doubt was disseminated generally through the body of the shale. Eroded slopes 

 of this shale are frequently closely strewn with these concretions, which remain 

 intact on the surface after the rains have washed away the readily disintegrated 

 matrix in which the concretions were originally formed and imbedded. The com- 

 mon form of the concretions is an irregular spheroid, and the usual sizes are from 

 half an inch to 4 or s inches in diameter. They usually have a very irregular 

 exterior surface, which in some may be described as irregularly botryoidal, as 

 mammillated, pitted, furrowed, ridged, or which may be so entirely irregular as to 

 defy any general description. Such are the greater number. Only in rare cases 

 are some found with a smooth outer surface. In some cases they approach a cylin- 

 dric form, and it appears that such concretions have started to form either in some 

 tubular cavities in the shale, or around some narrow cylindrical bodies buried in 

 the shale, for some such concretions still show traces of a centrally located tubular 

 cavity. Some concretions of this form were noted at a horizon in a red shale, which 

 at another place, a mile distant, contains sandy layers with fossil leaves, and the 

 suggestion prompts itself that these concretions have grown around roots or small 

 branches of plants originally imbedded in the shale. Some of these concretions 

 were seen to have had an inclined position in the strata. Another instance of 

 cylindric forms was noted in some sandy shale. In this case concretionary lime had 

 cemented the fine sand along a line vertical or slightly inclined to the stratification 

 planes, causing a cylindric or rather cone-shaped form to weather out from the shale. 



"In some places the concretionary material has been deposited along certain 

 structures in the shale, as along sandy layers, or in joints which have developed 

 in the clay. When these joints have opened up in the process the concretionary 

 material takes the form of irregular fissure veins. Some calcareous veins of this 

 kind were noted in a shale bank a short distance northeast of Electra. A system 

 of intersecting joints, closely set, seem to have been developed in the clayey matrix 

 next to some of the large concretions, with the result that the calcareous filling in 

 these fissures extends out and away from the concretions, and forms an irregular 

 network of ridges on their surfaces. The mammillated and irregularly botryoidal 

 surface on some concretions is clearly the result of an interruption of the concretion- 

 ary growth, and of a later resumption of the same, which has been more localized. 



"Internally the concretions in some cases show an irregular concentric structure, 

 and in one locaHty this was seen to consist of numerous smooth and even concentric 

 layers. More frequently they have radiating internal fissures which are filled by some- 

 what pure carbonate of lime, either in the form of crystalline calcite, of amorphous cal- 

 cite, or of a white powder of the same mineral . In other instances the internal structure 

 shows that some concretions are aggregations of many concretions of the smaller and 

 greatly variable sizes . " 



SANDSTONES. 



"The sandstones of the Wichita formation constitute something less than 20 

 per cent of the whole in the exposures. They are mostly light gray in color, though 

 some are red, dark gray, or mottled. 



