N. Knight — Dolomites of Eastern Iowa. 493 



The affinities of the fossil are obscure ; they seem to be with some 

 forms of the comprehensive ' genus ' Crioceras, but compared with 

 such Neocomian forms as Crioceras aegoceras, v. Koenen,^ and 

 G. capricornu (Roemer),^ which bear simple prominent ribs, the 

 present specimen has broader, more depressed whorls, and more 

 forwardly- inclined ribs than either of these species. It bears 

 a resemblance to some forms of the Upper Jurassic genus Simoceras, 

 but in that genus the transverse section of the whorl is more com- 

 pressed, wliilst the ribs on the peripheral area are strongly curved 

 forward, and the form of its septal surface is different. The last- 

 mentioned character suggests affinity with the Lower Cretaceous 

 forms of Bmivilletceras (I), mammillatum, D. Martinianiim, etc.). On 

 the whole we are inclined to refer the specimen to the ' genus ' 

 Crioceras with a query. 



As the two Cephalopods were not found at the same spot and under 

 the same conditions (the Belemnite being obtained in sihl, whilst the 

 Ammonoid was picked up in debris on the surface of the gTOund), 

 it is quite possible that they are not of the same age geologically, 

 although their lithological character leads one to infer that such is 

 the case. They indicate, however, the existence of Mesozoic rocks, 

 possibly of Neocomian age, in the anticlinal between Miram Shah 

 and Idak ; and now that the existence of fossils in this limestone 

 has been recorded it is to be hoped that at some future time other 

 specimens may be obtained which will enable the exact age of these 

 rocks to be determined. In conclusion, it maj^ be stated that the 

 fossils referred to in this note have been presented to the British 

 Museum (Natural History). 



VI. — The Dolomites, of Eastern Iowa. 

 By Nicholas Knight. 



THE experimental work of this investigation was done by Grace 

 D. Bradshaw in the chemical laboratory of Cornell College. 

 The purpose was to determine whether the silica exists in a free 

 condition or is in the form of a silicate ; also to ascertain whether 

 the iron is in the ferrous condition as carbonate or is in the form 

 of ferric oxide. The rocks abound in many parts of Iowa, and 

 belong to the Niagara formation. The stratified character even 

 in a small section is apparent, and the layers differ somewhat 

 in composition, as shown by the varying amounts of iron visible in 

 different portions. The rocks are used as building stone to manu- 

 facture quicklime and in MacAdam paving. 



1. To answer the first question as to the condition of the silica 

 six pairs of determinations were made as follows : — 



(a) A gram of the finely powdered rock was placed in a small 

 beaker and covered with a watch-glass, a small quantity of dilute 

 hydrochloric acid was added, and the carbonates were dissolved by 



^ Abhandl. d. k. Preuss. Geol. Landesaust. , etc., Neue Folge, Heft 24 (1902), 

 p. 328, pi. xxxvi. 



2 Ibid., p. 316, pi. xvi, figs. 1-4. 



