496 



SCIENCE 



[N. S. Vol. XXVIII. No. 719 



Dr. Milne, the veteran earthquake specialist, 

 read a paper on " The Duration and Direction of 

 Large Earthquakes," in which he called attention 

 to an apparent tendency of large earthquake 

 waves to travel farther to the west than to the 

 east, and to an apparent difBculty which they 

 encounter in getting across the equator. Professor 

 W. M. Davis discussed " Glacial Erosion in North 

 Wales," laying stress especially upon the preva- 

 lent corrie, the broad valley, and the hanging 

 side valley, as undeniable evidences of the impor- 

 tant eroding power of glaciers. 



Dr. Tempest Anderson made a report upon 

 " Changes in Soufrifere of St. Vincent " based 

 upon a recent trip to the island and upon his 

 earlier visit made just after the great eruption 

 oi 1902. Of special interest are the changes ob- 

 served in the torrent of hot mud which had filled 

 the Wallibu Valley to a height in places of more 

 than a hundred feet. The greater part of this 

 deposit has since been washed away, fragments 

 remaining, however, in a terrace 60 to 80 feet 

 high on the north side of the valley. In general 

 it may be said that in place of each of the earlier 

 valleys there are now found two parallel valleys 

 developed on either side of the mud streams which 

 have filled them. Each present valley thus has 

 for one of its walls the original valley wall and 

 for the other a cliff cut in the ash of 1902. 



Professor Lapworth contributed a report upon 

 important revelations made by excavation through 

 critical sections in Shropshire and North Wales. 

 A very interesting case of thrust and crush breo- 

 ciation in the Magnesian Limestone of County 

 Durham was presented by Dr. Woolacot. 



The most interesting feature of the meeting to 

 the geologists was a formal symposium on the 

 subject of mountain building, to which Professor 

 Joly, Sir Archibald Geikie, Professor Lapworth, 

 Professor Sollas and Professor Cole contributed. 

 Professor Joly in opening the discussion focused 

 attention upon the Alpine type of mountain, and 

 credited largely to Professor Lugeon the discovery 

 of the great overturned folds and thrusts of the 

 northern Alps. Radio-activity was brought into 

 the problem so as to connect the areas of moun- 

 tain elevation with areas of sedimentation. The 

 inunediate surface rocks were of such richness in 

 radium as to preclude the idea that a similar 

 richness would extend many miles inward. Now 

 as the sediments grew in thickness this original 

 layer was depressed deeper and deeper, yielding 

 to the load until at length it was buried to the 

 full depth of the overlying deposit. Here the law 



of increase of temperature with the square of the 

 depth came in, and the effect of the accumulated 

 sediment was thus a reduction in the thickness 

 of that part of the upper crust capable of resist- 

 ing a compressive stress. Along this elongated 

 area of weakness the crust found relief and was 

 flexed upwards. 



In continuing the discussion Professors Geikie 

 and Lapworth took the grovmd that the revelation 

 of Alpine structure must be largely credited to 

 earlier geologists, and especially to Heim and 

 Bertrand, whose observations and conclusions had 

 been elaborated and very ably presented by Pro- 

 fessor Lugeon. By Professor Lapworth mountains 

 were discussed especially in relation to the plan 

 of the earth, the distribution of the great moun- 

 tain ares, and the relation of the elevation of 

 shores to the depression of the neighboring sea- 

 bottom, in connection with which treatment he 

 paid a glowing tribute to Eduard Suess. 



Professor Sollas described a recent excursion 

 which he had made under the leadership of Pro- 

 fessor Lugeon in examination of the great over- 

 thrusts exhibited about the lake of Lucerne. The 

 frequent location of active volcanoes at the rear 

 of growing mountain ranges — on the side from 

 which the overthrust was exerted — was explained 

 by the use of Willis's law of competency of struc- 

 ture. The elevation of a competent layer of rock 

 relieved the pressure from underlying rock ma- 

 terial, thus allowing it to fuse and shift laterally 

 in the direction of the rear of the fold. 



The numerous excursions of the geologists to 

 points in the vicinity of Dublin were most in- 

 structive and offered greatest interest to students 

 of structural geology. The excursion of Saturday 

 to the Skerries under the leadership of Dr. Mat- 

 thies afforded the opportunity of examining a 

 section which revealed in great perfection all the 

 conunon types of folds, including small recum- 

 bent folds and overthrusts. The relation of gash- 

 ing and healing to the position of arches and 

 limbs was strikingly brought out. Professor Cole 

 and Mr. Seymour conducted another all-day ex- 

 cursion to the Devil's Glen and Glendalough 

 through some of the most picturesque sections of 

 County Wicklow. Here the contact zones of 

 great batholiths of granite in surrounding shist- 

 ose rocks were well displayed. Other interesting 

 excursions were conducted by Professor Rejmolds 

 and Mr. Muff. 



Wm. H. Hobbs 



Univeesitt op Michigan, 

 Attn Abboe, Michigan, 

 September 26, 1908 



