NORTH AMERICA AND THEIR VERTEBRATE FAUNA. 25 



bulk of the sand have been effectively left behind by the currents transporting the 

 sand. Nevertheless, some coarse sediments were found together with the sands 

 and the shale, but these are, as we might say, of indigenous origin, and have not 

 been transported from the same places as the rest of the material in the sands and 

 the shales. These indigenous coarse sediments may be designated as bone breccias 

 and mud-lump conglomerates. We shall describe the bone breccias in connection 

 with the limestones, of which they make a somewhat rare feature. The conglomer- 

 ate has been noted by all earlier observers in this field. Mr. W. F. Cummins very 

 aptly referred to it as a 'peculiar conglomerate.' It occurs in most frequent asso- 

 ciation with sand, quite often appearing as a basal laj'er under sandstone. Quite 

 frequently it forms separate layers interbedded in sandstone. In the described 

 sections it occurs interbedded in sand in 8 cases, and underlies sandstone and over- 

 lies shale in 3 instances. In 4 instances it was found interbedded in shale, which at 

 least in i case was slightly sandy and stratified. The assertion appears to be war- 

 ranted that the associations of this conglomerate indicate its formation in situations 

 where currents in the depositing waters were active. The conglomerate consists of 

 more or less rounded bodies of indurated and compact calcareous and argillaceous 

 material. Some of these are calcareous, others argillaceous or ochreous. They 

 measure from the size of sand grains to an inch and a half in diameter. Many 

 exhibit an obscure concentric structure, which is most apparent near the periphery. 

 Many have internal fissures, such as characterize clay ironstone concretions, and 

 calcareous concretions in clay beds. These balls, as we may call them, are more 

 or less uniform in size for different beds, having evidently been sorted by the trans- 

 porting currents. In the coarsest conglomerates noted they perhaps average half 

 an inch in diameter, and in the conglomerate of finest texture the individual pebbles 

 averaged less than one-tenth of an inch in diameter. Balls of the size of a pea 

 are common in samples where the sorting has been the most perfect. These balls 

 or pebbles are embedded in a matrix of clay or of sand, or of a mixture of these. 

 The matrix may be only a filling in the interstitial spaces in the conglomerate, but 

 it constitutes more than one-half of the rock. In some locahties the conglomerate 

 has evidently suffered alteration from mineralized ground water, in places substi- 

 tuting copper carbonate, ochre, or wad for the calcareous ingredients in the rock, 

 and in places merely precipitating these minerals in the original matrix. 



"Conglomerates like this are indeed not unknown in other formations con- 

 sisting largely of clay and shale. They have been noted by one of the present 

 authors in the late Cretaceous clays in Brewster County in Texas, and in the Penn- 

 sylvanian in Illinois and Iowa. In Ohio a somewhat similar rock has been noted 

 and described^ as a 'desiccation conglomerate.'" 



"In his paper on the 'Physical Origin of Certain Conglomerates,' J. H. 

 Gardner'' shows how water-currents which are overloaded with fine mud will form 

 balls which resemble concretions, and William B. Phillips'' has described how balls 

 of fine clay are formed in the troughs of the log washers in the treatment of brown 

 ores in Alabama. That most of the balls which make up these conglomerates have 

 been formed by a process of rolling appears likely from the concentric structure 

 which many of them have. But some of the pebbles have evidently withstood 

 more wear than mere mud balls can do. These must have been considerably indu- 

 rated originally, and they have the appearance of being true calcareous concretions. 

 It is believed that such pebbles in the conglomerates may have been washed out 



' J. E. Hyde, Amer. Jour. Sci., vol. xxv, 1908, p. 400. 



'' Gardner, Jour. Geol., vol. XVL, p. 452. 



■= Phillips, Iron Making in Alabama, Alabama Geological Survey, 2d ed., p. 55. 



