G. R. Wieland — American Fossil -Cycads. 219 



A tit. XXII. — A Study of some American Fossil Cycads. 

 Part I. The Male Flower of Cycadeoidea ; by G. P. 

 Wieland. (With Plates II-IY.) 



Introduction. 



The Mesozoic formations of the Pocky Mountain region, 

 especially around the Black Hills, have furnished few fossil 

 forms of higher scientific interest than the silicified trunks of 

 Cycads there preserved in great perfection. Most of these 

 specimens retain both their external features and internal 

 structure in such minute detail as to make possible a more 

 complete biological study of the entire group than has hitherto 

 been attempted. 



There is now in the Museum of Yale University a series of 

 these rare fossils, including several hundred individuals repre- 

 sented by complete, or nearly complete, trunks. For this 

 superb collection of fossil Cycads, Science is indebted to the 

 generosity and untiring zeal of Professor Marsh, who has also 

 given the writer the privilege of examining the entire series. 



The exact geological age of these Cycads is still in dispute, 

 but their general position is in the middle Mesozoic, and is most 

 probably Jurassic, as suggested by Professor Marsh in the fol- 

 lowing statement : 



" In the Pocky Mountain region, especially around the margin 

 of the Black Hills, a definite horizon likewise exists, in which 

 great numbers of Cycad trunks are found in remarkable pres- 

 ervation. These Cycads resemble most nearly those from 

 Maryland, found in what I term the Pleurocoelus beds of the 

 Potomac formation. In the Black Hills, the age of the hori- 

 zon has not been accurately determined. * * * Until recently 

 the Cycads of the Black Hills, although of great size and 

 remarkable preservation, have not been found actually in place. 

 In the large collection of Cycads belonging to the Yale 

 Mnseum, a few have been discovered apparently where they 

 grew, and systematic investigation will doubtless show that the 

 various localities where these fossils have been found around 

 the Black Hills are all in one horizon. The evidence now 

 available indicates its Jurassic age, and suggests that it is 

 essentially the same as that of the Cycad beds in Maryland, 

 which I regard as a near equivalent of the well-known Cycad 

 horizon in the Purbeck of England."* 



* The Jurassic Formation on the Atlantic Coast. — Supplement. — This Journal, 

 vol. vi, p. 115, August, 1898. See also, the present number, p. 229. 



Am. Jour. Sci. —Fourth Series, Vol. YII, No. 39. — March, 1899. 

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