SKETCH OF JOSEPH PRESTW1CH 259 



elevation of which one would ask one hundred thousand years, the 

 other might require for its more sudden elevation a force which 

 had taken the same number of years to accumulate its energies. 



Discussing in the Geological Society in 1889 the distribution 

 and probable age of some palaeolithic flint implements, Professor 

 Prestwich maintained that the removal of the material observed 

 indicated the existence of agents of greater force than those operating 

 under the present river regime. This closed up the time required 

 for the completion of the great physical phenomena, though the 

 author's inquiry tended to carry us further back geologically than 

 was usually admitted. 



In a paper read at the British Association in 1881 on the causes 

 of volcanic action, Professor Prestwich presented objections to the 

 generally accepted theory of Scrope that eruptions are a phenomenon 

 of steam, and held that water, instead of being a primary was only 

 a secondary cause of them — the primary cause being the rolling up 

 of the lava in consequence of pressure due to a slight contraction 

 of the earth's crust. The contact of this fluid lava with the water 

 stored in the crevices is followed by a flush of steam, and this by an 

 influx of water from underlying strata. These are converted into 

 steam and expelled, and the exhausted strata serve as a channel for 

 the influx of sea water into the volcano. A point is finally reached 

 when by the cessation of the shocks and excessive drainage the flow 

 of lava is effected quietly. A paper on Regional Metamorphism, 

 read to the Royal Society in 1885, presented a theory that there 

 exists, in the compression and motion of the strata which have always 

 accompanied the upheaval of mountain chains, a true cause for the 

 development of an amount of heat sufficient to produce one form of 

 metamorphosis — a form which can affect only particular regions — 

 and he would, therefore, in order to distinguish it from contact 

 and normal metamorphism, designate it as regional metamorphism. 



Some of Professor Prestwich's later views respecting the Glacial 

 period were presented at a meeting of the Geological Society in 

 May, 1887, when, after showing how the discoveries in the valley of 

 the Somme and elsewhere, twenty-eight years before, had led geolo- 

 gists who had previously been disposed to restrict the age of man 

 to exaggerate the period during which the human race had existed, 

 he proceeded to discuss the views of Dr. Croll on the date of the 

 Glacial period. In view of the recent observations in Greenland 

 of Professor Helland, Mr. Steenstrup, and Dr. Rink, showing that 

 the movement of ice in large quantities was much more rapid, and 

 consequently the denudation produced was much greater than had 

 formerly been supposed, he was disposed to limit the duration of 

 the Glacial epoch to from fifteen to twenty thousand years, in- 



