560 Notices of Memoirs — Prof. Beecher — Cambrian Fossils. 



the stratigraphy to suggest it. This must, therefore, be left to the 

 palaeontologists, and owing to the dearth of fossils the problem is 

 not an easy one for them to solve." In volume ix of the Missouri 

 Geological Survey (pt. iv, p. 52, Keyes, 1895) the Fredericktowu 

 dolomite ( = St. Joseph limestone) is referred to the Upper Cambrian 

 on account of the presence of Lingulella Lamhorni (Meek), but since 

 this species is peculiar to the horizon, and the genus has a much 

 wider range, this correlation is not established. A general statement 

 is made by Keyes regarding this region (I.e., p. 44) that " No strata 

 younger than the Cambrian are believed to be represented. But 

 few fossils have been found in the rocks of the area, so that the 

 faunal evidence as to geological age is somewhat meagre." The 

 present collection of fossils, made by Mr, Nason, indicates that the 

 entire series is older than the Lower Silurian (Ordovician), and that 

 at least the upper portion probably belongs to the Upper Cambrian. 

 All but one species of the fossils were obtained from the lower 

 members of the Potosi limestones, and since this is the topmost 

 formation of this region its correlation is of the first importance. 

 The fossils occur abundantly in the limestone and conglomerate 

 beds, and more sparsely in the sandstones. They consist chiefly 

 of fragments of trilobites, with a few brachiopods and other forms. 

 Lithologically, there is a very close resemblance between these 

 fossil-bearing beds and those of a similar horizon in the Black Hills 

 of South Dakota. Limestones, limestone conglomerates, and sand- 

 stones of the same appearance are found in both sections. Faunally, 

 there is a suggestion of affinity with the Potsdam fauna of Wisconsin 

 and Texas. A careful comparison, however, reveals that these 

 resemblances are more general than specific, and that the species 

 seem to be distinct. Nevertheless, the facies of this fauna seems 

 to indicate Upper Cambrian, though further studies with additional 

 material may show it to belong to the middle member. 



Owing to the small number of specimens in the present collection, 

 the number of species is necessarily limited. It will doubtless be 

 considerably increased by future collections. Among the trilobites 

 the genera Ptyclwparia, Ptychaspis, Chariocephalus, and Crepicephalus 

 are more or less clearly identifiable. A species of Chariocephalus 

 closely agrees with the C. onustiis of Whitfield. 



The species of brachiopods seem to be fairly abundant, especially 

 an orthoid shell resembling in some respects Billingsella. It occurs 

 in the shaly partings between the layers of limestone. A species 

 of Acrotreta and Lingulella are common both in the limestones and 

 arenaceous beds. 



Hyolithes primordialis, Hall, and a small species of Platyceras also 

 occur in the limestones, together with segments of cystidean or 

 crinoidal columns. 



Abundant remains of a linguloid shell are found on the lower, 

 or La Motte, sandstones constituting the basal member of the clastic 

 rocks of the section. Making allowances for diff'erent conditions 

 of preservation, this species may be identified with the Lingulella 

 Lamhorni of Meek, which occurs in some green shales of the same 



