39 



a blowpipe — a weapon used for shooting animals with poisoned 

 darts — were shewn in some particularly fine slides. The interest of 

 the lecture was still further increased by the exhibition of a collection 

 of native weapons, instruments, &c. 



_ A lecture given on the ist May, 1909, by Dr. Ord, 



e ^ rea chair being taken by Dr. Crallan. Beginning 



efcsinian -with a few general remarks on the origin and 



d 't " sources of earthquakes. Dr. Ord remarked that the 



* two districts ot Great Britain where earthquakes 



ueo^ogica most common (though fortunately only slight 



Causes. ones) are the portion of Herefordshire near the 



Malvern Hills and the line of the Caledonian Canal in Scotland — 

 in each case near hills or mountains composed of very ancient or 

 igneous rocks. On the Caledonian Canal lies a great fault, or old 

 dislocation of the strata, which is a common feature of unstable 

 areas. The line of mountains in the West of America was mentioned 

 as a district where earthquakes are common, and as exhibiting 

 features usual in earthquake areas, viz: — lofty mountains, proximity 

 to the sea with deep ocean beds, frequent changes in the level of the 

 land, frequency of faults, and the presence of volcanoes. The 

 lecturer explained the instruments in use for recording earthquakes 

 and said that these disturbances usually proceed from a point about 

 15 miles below the surface, and that a point immediately over this 

 is the seat of maximum intensity. From this point the disturbance 

 proceeds in regular waves, of less intensity as they recede from the 

 centre. The waves from Messina reached the Kew observatory in 

 four minutes after the shock began. Messina lies on the line of 

 mountains formed by the Appenines and the Peloritan Hills of 

 Sicily, once continuous. These mountains are chiefly of old crystal- 

 line rocks, though near Messina we have the more recent strata, 

 chiefly Miocene and Pliocene, deposited upon the older rock ; in the 

 Pliocene strata, 4,000 feet above the sea, we find recent shells, which 

 points to tremendous upheavals in recent geological times, and in- 

 stability of the earth's crust in this area. On the western slope of 

 the mountain range is a great fault which is constantly shifting, the 

 line of fracture passing close to Reggio and Messina, and it is this 

 which causes the earthquakes : they have probably been occurring 

 for long past ages and may continue to do so at intervals for many 

 years to come. A number of photographs of Messina, showing the 

 ruin that had befallen it, were shown, and Dr. Ord concluded by 

 remarking that, though investigation into the theory of earthquakes 

 does not enable us in any way to control them, it helps us to see how 

 best we may mitigate their effects, by building houses low and light 

 — least likely to sustain damage themselves and to cause further 

 damage in their fall. 



