Observations on Earthquakes in South America. 153 



10. The inflammable pit-gases exhibit a very different de- 

 gree of inflammability when mixed with atmospheric air, ac- 

 eording to the different proportions they contain of nitrogen, 

 carbonic acid gas, and defiant gas. The two first gases di- 

 minish, the last increases their inflammability. The larger 

 the amount of atmospheric air with which they can be mixed 

 without losing their detonating power, the more dangerous are 

 the explosive mixtures formed by them in coal-mines. 



Observations on liecent Earthquakes on the West Coast of 

 South America:'" By Mathie Hamilton, Esq., formerly 

 Surgeon to the Potosi, Paz, and Peruvian Mining Company, 

 &c. Communicated by the Avithor. 



The west coast of South America, between the northern frontier of 

 Peru and the south of Chili, includes an extent of territory .3000 miles 

 from north to so-ith. 



Rain is very seldom seen on the coast of Peru, which is a desert, with- 

 out water, vegetation, and inhabitants, except at a few spots, where a tor- 

 rent from the Andes conveys the melted snow and rain, which falls in 

 immense quantity on those sublime heights during the hotter months of 

 the year, when almost every day after meridian a tempest of lightning 

 aud thunder, with rain, hail, or snow, is experienced, which causes the 

 ravines to convey a flood to the arid plains below, which in some places 

 reaches the sea, but in most parts is lost in the desert. 



Along this vast extent of coast, at the distance of ten to thirty leagues 

 from the Pacific Ocean, the mountains of the western Cordillera rise like 

 an enormous rampart, to the altitude of 12,000 to 20,000 feet above 

 the level of the sea, — many of their summits are shrouded in perpetual 

 snow, glittering under the sunbeams, above the ordinary region of 

 clouds and storms. Those mountains, in numerous parts, exhibit evi- 

 dence of volcanic action, now dormant, but in some places they are still 

 in operation, giving out smoke, and occasionally flame. From time im- 

 memorial, this portion of the earth has been subject to destructive vol- 

 canic eruptions and dreadful earthquakes. I will notice some of the more 

 recent phenomena which have come under our immediate observation, 

 and in a more special manner the terrible earthquake of 18th September 

 li',:i.*5, which shook an extent of country equal to twice that of Great Bri- 

 tain, destroying the city of Tacna and other places in Peru. To under- 

 stand more clearly what follows, I briefly notice a few geographical and 



• Read before the British Association nt Glasgow. 



