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IOWA ACADEMY OF SCIENCES. 



very slightly by the cubic faces. In the direction of the crystallographic axes the 

 octohedral corners have become greatly extended from the center forming long, 

 series of octohedrons partly inclosed in one another, the terminal one in each of the 

 six sets being almost perfect except on the end of attachment. With one series 

 pointing directly in front and the opposite one directly behind the remaining arms 

 forms a slender Swiss cross, whose dimensions are sometimes from four to six 

 inches. These may be regarded as a large number of sub-individuals forming par- 

 allel growths, each individual represented by a thin plate between each pair of re- 

 entering angles. The terminal octohedrons are often an inch along the edges. 

 But if the skeleton were completely filled out the octohedral edges would measure 

 five inches or more. 



Calciie. — Among the " geodes" from the Keokuk limestone of southeastern 

 Iowa, calcite is found in many different forms; a large variety of rhombohedrons 

 and scalenohedrons and their combinations being represented. A particularly inter- 

 esting occurrence is that of very perfect fundamental or cleavage rhombohedrons 

 (R), with the planes of no other forms present. This is one of the rarer forms of 

 the mineral under consideration and the known occurrences are very limited. 



Gypsum. — Crystallized gypsum is a rather common occurrence in many of the 

 coal measure shales of central Iowa. Some specimens discovered a short time ago 

 seem worthy of special note since they are unusually perfect and are found in large 

 numbers. The edges are sharply .cut and faces brilliant. The crystallographic 

 forms are oo P co, P oo, and oo P. They assume the well known diamond shapes, 

 with beveled edges. Not unfrequently individuals contain very distinct "shadow" 

 crystals. 



In some localities the crystals form swallow-tailed twins and become greatly 

 elongated in the direction of the vertical axis. Examples of this kind sometimes 

 attain a length of six to eight inches. 



MiUcrite. — For a number of years past there has been noted occasionally in 

 "geode collections" examined from different parts of Lee county in southeastern 

 Iowa, certain specimens containing clear calcite crystals, traversed in different direc- 

 tions by minute yellowish filaments after the manner of Vaei:Am\\\&v fleches d' amour 

 —the rutile needles in quartz. Recently in opening a large quarry near the city of 

 Keokuk, in the compact Keokuk limestone some feet below the regular "geode 

 bed" numerous cavities were encountered varying from three to twenty inches 

 in size. These hollows have large, thickly set rhombohedrons of calcite jutting 

 out towards the center. The faces are brightly polished and the edges are 

 sharply cut. On some of the calcites have been found beautiful tufts of closely 

 arranged, brass-yellow needles of millerite pointing from the center of attach- 

 ment, in all directions to a distance of one-half to two and one-half inches. 

 In some of the examples the tutts are made up of hundreds of filaments, often so 

 close together that the needles of the different branches are interwoven, forming a 

 dense matted mass. Often a large, perfectly transparent calcite has a tuft of long 

 "millerites completely inclosed in it; or a part of the tuft may be embedded in the 

 lime crystal, the extremities of the needles left projecting outside. 



The Keokuk occurrences are believed to be the most beautiful ever found in 

 this country, if not in the world. 



Mr. C. A, Flannery, of Keokuk, has very lately found another "nest" of similar 

 geodes containing millerite. One specimen of calcite covered thickly with needles 

 of the nickel sulphide weighed over fifty pounds. Still more recently equally fine 

 specimens of millerite have been reported from Ft. Madison. 



