PALEONTOLOGY. 455 



But an additional petrified type has at last been found inthecycad 

 horizon. Last year Professor Knight, of Laramie, secured from the 

 Lower Lakota of northwestern Wyoming the silicified stems of the 

 strange pseudo-tree-fern Tempskya. This is the second occurrence 

 for North America, much less well silicified forms having been described 

 from the Potomac of ]\Iaryland several years since by Berry. Though 

 thus far so rare for North America, Tempskya is of wide and long-known 

 distribution in the European Lower Cretaceous. Briefly, this fossil 

 fern, of structure little more complex than a bracken, branched re- 

 peatedly^, to end in a crown-like summit, while innumerable aerial 

 rootlets interlaced to form the quite compact pseudo stems, which 

 may reach a foot in diameter and 10 feet or more in height. An 

 exact parallel is afforded by an isolated Javanese species of Hemitelia, 

 illustrated in the Buitenzorg Annals; while other species ot the genus, 

 more like other ti'ee-ferns, reach south latitude 30° in the Natal veldt 

 country, the general habitat of the cycad Stangeria. 



The general inferences as to the climate of the Northwestern cyca- 

 deoid belt are thus slightly broadened by unexpected comparison 

 with the South African cycad realm. But while from its Javanese 

 occurrence, Hemitelia runs more toward the tropics, the heavy- 

 stemmed Cretaceous cycadeoids have the appearance of plants able 

 to withstand alike drought and snowfalls — probably more marked 

 than those rarely reported from the limit of cycad occurrence in 

 South Africa at south latitude 32° to 33°. 



From the representative material of the Lakotan Tempskya trunks, 

 kindly sent by Professor Knight, thin sections have been cut showing 

 remarkably clear preservation. The stems at least 15 centimeters in 

 diameter bore close-set foliage and have the same thick-set mat of 

 pendent rootlets as the English and other European species, from 

 which there is only specific separation. 



SEVERAL PHENOMENA OF SILICIFICATION. 



A recondite feature of the cell-walls observed only once in the 

 foregoing Tempskya may have a bearing on the process of silicifica- 

 tion. There are apparently present minute asymmetric rods with a 

 clouded or little-defined enveloping zone, analogous to the siliceous 

 rods isolated from cell-walls of living plants by Brown. And such 

 rods, as suggested by Professor Charles S. Hastings in confirming 

 their siliceous nature, might afford initial nodes of silicification. If 

 so, plants with a larger silica content must tend to be the more sus- 

 ceptible to silicification. 



But whether this view is correct or not, in the Como, silicification 

 of the cycadeoids and conifers closely associated with the dinosaurs 

 was a direct process. At the ''Cycadella" locality in the Freeze-Out 

 Hills, the large conifer stems may be soft and carbonaceous at one 



