STRATIGRAPIIIC TAXC^NOMY G8o 



the two was satisfactorily indicated, but as most of the occurrences are of 

 merely the residual mantle following deep surface decay of the original 

 magnesian limestone beds, the contact between them is seldom seen. 

 Chert conglomerate is frequently found at this horizon, and at several 

 localities unstratified accumulations of brownish, red, and green clays 

 were associated with the conglomerate pebbles. At other places the pre- 

 sumably basal agglomerate has been silicified into rough masses of chert. 

 Most of the occurrences, finally, are confined to old downwarps, which 

 probably formed small embayments of the shoreline at this and subse- 

 quent times. 



In the early part of my investigation of the Ozark uplift this over- 

 lying bed was assumed to be a locally fossiliferous upper bed of the Jef- 

 ferson City dolomite. With the progress of the work this interpretation 

 became more and more improbable and is now abandoned. The true 

 significance of the fauna finally became clear when comparisons proved 

 its general identity with early to middle Canadian faunas found in the 

 lower part of the Yellville in northern Arkansas, beneath the middle of 

 the Arbuckle limestone in Oklahoma and in approximately correspond- 

 ing deposits in central and western Texas, in the Wells Creek uplift of 

 central Tennessee, at many points in the Appalachian Valley from Ten- 

 nessee to Pennsylvania, in the Champlain Valley, and in Newfoundland. 

 The most characteristic fossils of this widely distributed series of Cana- 

 dian deposits are the horn-shaped opercula, for which the generic name 

 Ceratopea is later on proposed. Six or seven distinguishable species of 

 these opercula are now known, but the shells to which they belonged have 

 not been preserved. The associated gastropods and cephalopods, of 

 which some twenty species have been collected in Missouri, are closely 

 allied to and in part the same as Beekmantown limestone fossils described 

 from New York and Canada by Whitfield and Billings. 



The OzarJi-ian in the southern Appalachian Valley. — As developed in 

 central Alabama and east Tennessee, the Ozarkian sequence, beginning 

 below and passing upward, comprises the following formations : 



Briarfield dolomite (new). — It is 1,250 feet thick, well exposed in 

 Cahaba Valley along Six-Mile Creek, 10 miles southwest of Montevallo, 

 Alabama. Not observed elsewhere. Section studied in 1910 by Charles 

 Butts, whose notes have been generously placed at my disposal. Accord- 

 ing to his observations, the Briarfield follows about 1,100 feet of thin- 

 bedded amorphous blue limestone, with earthy streaks on weathered sur- 

 face. Fossils procured from finely granular limestone at the base of this 

 underlying formation indicate its age as upper Cambrian. Contact with 

 the base of the Briarfield, though not fully exposed, apparently sharply 

 defined. 



XLII— Bull. Geol. Soc. A.m., Vol. 22, 1910. 



