Notices of Memoirs — A Fossil Cycad, Portland. 319 



The apical bud of recent Cycads is occasionally capped by a mass 

 of loose hairs, and there is the closest jDOSsible resemblance between, 

 the bud of this Portland stem and that of such a recent Cycad as 

 JEnceplialartos Altensteinii, Lehm., a species well represented in the 

 tropical-house at Kew. 



Fig. 2. — Apical bud of Ctjcadeoidea gigantea, Se^w^ard. 



The materia] of which the specimen consists is highly siliceous ; 

 the central portion exhibits no trace of plant-structui-e, and is com- 

 posed of cherty rock, but portions of the more external tissues are in 

 some places exceedingly well preserved. The description of the 

 structure of the petiole bases, and that of the mass of interpetiolar 

 tissue, as given in the more detailed account of the stem, demon- 

 strates a striking similarity between the anatomy of the genus 

 Bennettites and that of the new fossil. In the absence of any definite 

 trace of reproductive organs, the Portland stem has been placed in 

 Buckland's genus Cycadeoidea, and named Cycadeoidea gigantea. 

 As regards the exact affinities of the species, it is impossible, 

 without the evidence of the reproductive organs, to speak with 

 certainty as to its precise position. There is, however, no sufficient 

 reason for regarding the stem as essentially distinct from such a type 

 as is represented by Bennettites Gihsonianus, so far as concerns its 

 position in a system of classification. 



II. — The Pleistocene Ice-sheet in Nokth Amekioa : Englaoial 

 Drift. By W. 0. Ceosbt.^ 



Probable Early History of the Pleistocene Ice-sheet. 



RECENT researches iu North America tend to show that an 

 ice- sheet may over a considerable part of a glaciated area 

 have been formed in situ by snow accumulation. 



A general refrigeration of the climate in mountainous districts, 

 due chiefly perhaps to a marked elevation of the northern part 

 of the continent, had led to the development of glaciers of the 

 Alpine type in the higher valleys. These glaciers became confluent 



^ Abridged from the Teclmologij Quarterly, vol. ix, Nos. 2 and 3. (Boston, 1896.) 



