153 



HARDWICKKS SCIENCE-GOSSIP. 



specimens make a handsome addition to the herbarium 

 and are easy to arrange. 



C. Parkinson, F.G.S. 



Genus Dentaria (L.). (Coral Root.) 



Plants of the cruciferous order. Having 4 sepals, 

 free ; petals 4, opposite, entire ; stamens 6, 4 long 

 and two short ; ovary free ; carpels 2 ; ovules sus- 

 pended. Fruit long (silique), compressed, not nerved, 

 opening by valves ; root scales coral-like, fleshy and 

 irregular, with numerous fibres ; the stems of the plant 

 springing from the point of the tooth-like scales. 



1. D. pinnala (Lam.), stem upright, leafless at the 

 lower part 3-4 leaves alternate, not surrounding 

 the terminal flower ; pinnate, the segments being 

 5-9, lanceolate, pointed and boldly serrated, flowers 

 large, lilac or white. Plant somewhat succulent, 

 growing in moist situations. March, April. 



2. D. digitata (Lam.), D. pcntaphyllos (Waldst.), 

 similar to last species, and often growing together 

 with it. Readily identified by the palmate leaves ; of 

 5 ovate-lanceolate segments ; flowers rose, lilac or 

 white. March, April. 



3. D. bulbifcra (L.), a rarer plant in Switzerland, 

 but the only species found in England. The upper 

 leaves are entire, serrated, and alternate ; the lower 

 leaves ternate or rarely palmate, the bulbules form at 

 the axis of leaf and stem. They are of a purplish 

 hue, drop off at a certain period, and develop into 

 separate plants. April, May. 



4. D. polyphylla is another species given by 

 Bouvier (Flore desAlpes), leaves verticillate, probably 

 a variety of D. pinnata ; flowers white, turning yellow 

 as they fade. April, May. 



THE DATE, DURATION, AND CONDITIONS 

 OF THE GLACIAL PERIOD WITH 

 REFERENCE TO THE ANTIQUITY OF 



MAN. 



THE following is a summary of a very important 

 paper recently read before the Geological 

 Society by Professor Joseph Prestwich, M.A., F.R.S., 

 F.G.S. 



After showing how the discoveries in the valley of 

 the Somme and elsewhere, twenty-eight years ago, 

 led geologists who had previously been disposed to 

 restrict the age of man, to exaggerate the period 

 during which the human race had existed, the author 

 proceeded to discuss the views of Dr. Croll on the 

 date of the Glacial epoch. Dr. Croll, who had at 

 first referred this to an earlier phase of orbital 

 eccentricity, commencing 980,000 years ago, subse- 

 quently regarded it as coinciding with a minor period 

 of eccentricity that commenced 240,000 and ter- 

 minated 80,000 years since. This last estimate was 

 chiefly supported by the amount of denudation that 

 had subsequently taken place. 



The efficacy of the increased eccentricity of the 

 earth's orbit in producing the cold of the Glacial 

 epoch was shown to be very doubtful ; for as similar 

 changes in the eccentricity had occurred 165 times in 

 the last 100 millions of years, there must have been 

 many glacial epochs in geological times, several of 

 them much more severe than that of the Pleistocene 

 period. But of such glacial epochs there was no 

 valid evidence. Another inference from Dr. Croll's 

 theories, that each glacial epoch consisted of a 

 succession of alternating cold and warm or inter- 

 glacial phases was also questioned, such alternations 

 as had been indicated having probably been due to 

 changes in the distribution of land and water, not to 

 cosmical causes. The time requisite for such inter- 

 glacial periods as were supported by geological 

 evidence was more probably hundreds than thousands 

 of years. 



Recent observations in Greenland by Professor 

 Helland, Mr. V. Steenstrup, and Dr. Rink, had 

 shown that the movement of ice in large quantities 

 was much more rapid, and consequently the denu- 

 dation produced much greater than was formerly 

 supposed. The average rate of progress in several of 

 the large iceberg-producing glaciers in Greenland 

 had been found to be thirty-six feet daily. Applying 

 these data and the probable accumulation of ice clue 

 to the rainfall and condensation to the determination 

 of the time necessary for the formation of the ice- 

 sheet, the author was disposed to limit the duration 

 of the Glacial epoch to from 15,000 to 20,000 years, in- 

 cluding in this estimate the time during which the cold 

 was increasing, or pre-glacial time, and that during 

 which the cold was diminishing, or post-glacial time. 



Details were then given to show that the estimate 

 of one foot on an average being removed from the 

 surface by denudation in 6000 years, on which 

 estimate was founded the hypothesis of 80,000 years 

 having elapsed since the Glacial epoch, was insuffi- 

 cient, as a somewhat heavier rainfall and the dis- 

 integrating effects of frost would produce far more 

 rapid denudation. It was incredible that man should 

 have remained physically unchanged throughout so 

 long a period. At the same time the evidence 

 brought forward by Mr. Tiddeman, Dr. Hicks, and 

 Mr. Skertchly of the occurrence of human relics in 

 pre-glacial times, had led the author to change his- 

 views as to the age of the high-level gravels in the 

 Somme, Seine, Thames, and Avon valleys, and he 

 was now disposed to assign these beds to the early 

 part of the Glacial epoch, when the ice-sheet was 

 advancing. This advance drove the men who then 

 inhabited western Europe to localities such as those 

 mentioned which were not covered with ice. Man 

 must, however, have occupied the country but a short 

 time before the land was overwhelmed by the ice- 

 sheet. The close of the Glacial epoch, i.e. the final 

 melting of the ice-sheet, might have taken place from 

 Sooo to 10,000 years since. Neolithic man made 



