ANALYTICAL ABSTRACTS. 755 



in a series of schists and graywacke :orresponding in point of ages with the 

 phyllades de Saint L6 (pre-Cambrian). 



Preservation. — The radiolaria were, as is usual with the Palaeozoic forms, 

 very badly preserved, so that a great many sections were necessary to obtain a 

 few good specimens. Even these were so delicate and so surrounded and filled 

 with fragments of carbonaceous material as to greatly increase the difficulty 

 of observation. The outlines and details of structure were nevertheless, as 

 the plates indicate, so complete in many instances as to leave no doubt as to 

 the nature of the organisms. The skeletal silica is often found in the form 

 of opal, often replaced by carbon. 



Forms found. — Among the number of forms whose generic place could be 

 determined beyond doubt are mentioned : Cenosphaera, Carposphaera, Xipho- 

 sphaera, Stanrosphaera, Acanthosphaera, Cenellepsis, Spongurus, Tripocalpis, 

 Tripilidium, Tripodiscium, Archicorys, Cyrtocalpis, Dictyocephalus, Setho- 

 capsa, Dicolocapsa, Theocampe ; representing the sub-orders, Sphaeroidea, 

 Cyrtoidea, Prunoidea and (not determinable as to genus) Discoidea. 



Criticisms. — The author takes up in detail objections that have been raised 

 against the existence of radiolaria in pre-Cambrian strata as (i)the invisibility 

 of the reticulated, skeletal structure, (2) the impossibility of seeing the sili- 

 ceous tests imbedded in quartzite, (3) the uniform regularity of the figures 

 observed and the size of the observed forms in comparison with known radio- 

 laria, (4) the contact or intergrowth of the pre-Cambrian forms, (5) their simi- 

 larity to foraminifera. 



Character of the f arena. — A discussion of the grouping and comparative 

 abundance of various species follows, and then a comparison of the pre-Cam- 

 brian fauna with the radiolaria of the Silurian and of the present. E. C. Q. 



The Niobrara Chalk. By Samuel Calvin, Iowa City, Iowa. (American 

 Geologist, September, 1894.) 

 The presence of the Niobrara chalk has been demonstrated at various 

 points in Iowa as far east as Auburn, in Sac county, while fossils in the drift 

 indicate its former existence at points much farther east than this. The 

 paper deals chiefly with the characteristics of the formation as exhibited east- 

 ward from the mouth of the river from which it takes its name. In their typ- 

 ical development the strata are soft, calcareous deposits lying in massive beds, 

 and exhibit all the characteristics of chalk. The beds represent the final 

 stage in a progressive subsidence, when the mechanical sediments gave place 

 to those of organo-chemical origin, with waters clear and moderately deep, 

 and the shore line probably a hundred miles to the eastward. An upward 

 movement began before the close of the Niobrara age. The most conspicu- 

 ous invertebrates are Inoceramus problematicus and Ostrea congesta. Numer- 



