750 JOURNAL OF GEOLOGY. 



Other papers by Mr. Keyes are : " Annotated Catalogue of 

 Minerals," and " Bibliography of Iowa Geology." 



Professor Calvin's paper is devoted to the Cretaceous deposits of 

 Plymouth and Woodbury counties. In the region studied these beds are 

 found to be sharply divisible lithologically into two divisions, a lower 

 consisting of soft sandstones, with bands of hard ferruginous concre- 

 tionary nodules, and variegated, often parti-colored clays, the latter 

 greatly predominating and resting upon these a white or yellowish 

 chalk, somewhat indurated in places into a soft fissile limestone. The 

 first is White's Woodbury sandstones and shales, and the second is his 

 Inoceramus beds. Following Meek and Hayden, Professor Calvin 

 makes a threefold division of the beds, by drawing a somewhat 

 arbitrary line about forty feet below the base of the Inoceramus beds. 

 The lowest division contains impressions of leaves and a meagre 

 brackish water fauna. This he correlates with the Dakota group. The 

 second or middle division of dark colored calcareous shales, containing 

 marine mollusks, associated with the vertebrae and teeth of bony fishes, 

 and the skeletons of marine saurians, is the Fort Benton group of 

 Meek and Hayden. The upper or Inoceramus beds represent the 

 Niobrara of the same authors. During this epoch the Cretaceous sea 

 had its farthest eastward extension, probably reaching as far as the 

 Mississippi river in northeastern Iowa. 



Mr. Beyer's paper is entitled Ancient Lava Flows in the Strata of 

 Northwestern Iowa, and relates to the discovery in a well at Hull, 

 Sioux county, of typical quartz porphyry at a depth of 755 feet. 

 Microscopical study shows it to have a pronounced flow structure, while 

 the quartz crystals' show the effects of magmatic corrosion, and, in 

 some cases, fracturing with discordant orientation of the fragments, 

 from which it is inferred that the magma was semi-viscous and under 

 great pressure when the flow took place. In the drilling, the eruptive 

 rock was found to alternate with sandy strata, showing evidence of 

 metamorphism down to 1,200 feet. Two hypotheses are advanced to 

 account for the flows : (1) That they took place in Paleozoic times, 

 perhaps Carboniferous, the lava being periodically poured out over 

 the old sea bottoms ; and (2) that the whole series of flows was con- 

 temporaneous, and in point of time post-Carboniferous. In this case 

 the intercalations may be regarded as intrusive sheets, following the 

 lines of least resistance and forcing themselves between the strata. 

 Most probability seems to attach to the latter view. 



