﻿94 VEGETATIVE FEATURES. 



pinnule structure of Cycadeoidea ingens will be afforded. In summation it is then to 

 be noted that the prefoliation and general form of the frond of C. ingens agree in all 

 essential features with existing cycads ; while it is not unlikely that among the 

 pinnules of species as yet not figured or examined there may be one or several with 

 microscopic structures quite completely homomorphic to those of Cycadeoidea 

 ingens or other cycadeoidean forms. Were one to adjudge the taxonomic position 

 of the fossil species on the basis of its foliage only, one might, bearing in mind 

 the general absence of scale leaves, place it near Macrozamia or Encephalartos. 



ON YALE CYCAD NO. 208 (A COTYPE OF CYCADEOIDEA INGENS) AND ITS 



ADVENTITIOUS LEAVES. 



(Figs. 44 and 50, with Photographs G-8 of Plate XIX.) 



Trunk No. 208 of the Yale collection of fossil cycads was discovered by the 

 writer in September, 1898, under somewhat exceptional circumstances. It is a 

 specimen of Cycadeoidea ingens, and is mentioned in the Nineteenth Annual Report 

 of the United States Geological Survey, page 564, by Professor Ward, who, in 

 company with the writer, inspected it while still in situ, about 4^ miles east by 

 south of Piedmont, South Dakota, at the north end of the Cycad Valley, as the 

 deep depression in the Piedmont-Black Hawk cycad area may be called. A map 

 of this region is given in the Nineteenth Annual Report of the United States 

 Geological Survey, opposite page 564, with a brief discussion of the stratigraphical 

 relations. At the south end of the valley is the old cycad locality, 3 miles north of 

 Black Hawk, from which most of the specimens from this section of the Black 

 Hills Rim were obtained. As coming from the north end of the Cycad Valley, the 

 present trunk is of distinct value in extending the Black Hawk cycad locality as 

 at first known, and thus aiding to delimit the extent and character of the cycad 

 horizon to which it belongs. Also, being the only specimen from the Piedmont 

 region found nearly or wholly in place, a brief mention of the segment of the Black 

 Hills Rim from which it came may be interpolated. As very well shown in the 

 views of the Piedmont-Black Hawk region given on plates xlatii-l, the "rim" is 

 here quite complex ; while following the huge escarpment of Jurassic and Cretaceous 

 rocks forming the outer wall beyond the Triassic " Red Valley " extending all 

 round the Black Hills, as so well known to all students of the geology of that 

 wonderfully interesting region, there is a deep syncline followed by a prominent 

 anticline producing a series of valleys and ridges. East of Piedmont the series of 

 rim ridges as thus made up is nearly 4 miles wide. But these ridges disappear to 

 the south and southeast, the rim again becoming a simple main mouoclinal ridge 

 northeast of Black Hawk. There is thus formed a triangular area of rough and 

 broken or hilly rim country with its base east of Piedmont and its vertex about 2 

 miles north of Black Hawk. From this vertex the Cycad Valley extends north- 

 ward 3 miles, being deeply scooped out of the eastern or outer and anticlinal portion 

 of the rim, with the marine Jurassic and finally the " red beds " exposed at its base. 



After making an examination of the old locality at the south end of the valley, 

 the writer decided that cycads might perchance be found at the northern end. And 

 as so much interest attaches to the relative position of the Atlantosaurus and cycad 

 horizons, repeated efforts were made to find material that would in a measure confirm 



