294 



SCIENCE. 



[N. S. Vol. VIII. No. 192. 



maximum deposition forming the thickest 

 mass (58,000 feet) of Pliocene in North 

 America. The mountains of British Co- 

 lumbia are believed to have been at a 

 higher level than now, as it is supposed that 

 Vancouver and Queen Charlotte Islands 

 probably formed part of the mainland. 



At or near the close of the Pliocene the 

 Sierra Nevada increased in height by the 

 tilting of the whole block westward. New 

 river valleys, cut through the late basalt 

 sheets of the Sierras, are much deeper than 

 the older valleys excavated in Cretaceous 

 and Tertiary times, owing to the greater 

 height of the mountains and to the conse- 

 quent greater fall of the streams. At this 

 time the Wasatch Mountains and high pla- 

 teaus of Utah and Arizona were again up- 

 raised, and the great mountain barrier of 

 the St. Elias, in southeastern Alaska, was 

 likewise thrown up. At this time also, or 

 perhaps later, the mountains of British Co- 

 lumbia were probably raised still higher.* 

 It will be seen from this that the present 

 topography of the western border of our 

 continent including Central America and 

 the Isthmus of Panama belongs to a new 

 topographic era, and fully substantiates the 

 view that the fauna of these regions is very 

 recent compared with that of the Atlantic 

 border, and that the number of nascent or 

 incipient species is much greater. 



Alpheus S. Packard. 



Beown Univeesity. 



( To ie concluded. ) 



EABTHQUAKES. 

 Commandant Montessus de Ballorb, of 

 the French Army, is well known as an 

 authority on earthquakes in general, and 

 especially on the earthquakes of Central 

 America, where he resided for a consider- 

 able time some dozen years ago. Besides 

 his own observations he has discussed 

 thousands of others, collected by himself 



* JoKraaZ GcoL, IV., pp. 882, 894, 897 and 898. 

 (Quoted from Drake.) 



or taken from the extended lists of Mallet 

 (B. C. 1606 to A. D. 1850), Perrey, Fuchs, 

 etc. All of the available material has been 

 sifted and examined, and then discussed in 

 a scientific fashion, to bring out whatever 

 general laws may underlie the statistics. 



A collection of some of M. Montessus' 

 pamphlets has lately come into my hands.* 

 They deserve anextended review, but, failing 

 this, the following notes may be of interest. 



The relations between the topography of 

 a country — its topographic relief— and the 

 frequency of its earthquakes has been de- 

 duced from 98,868 records of shocks at 

 6,789 centers distributed ,in 353 regions of 

 the globe. The most general statements 

 that can be made are as follows : 



" Eegions of great earthquake frequency 

 lie near the greater lines of corrugation of 

 the earth's crust." 



" In any group of adjacent seismic regions 

 the earthquake frequency is greatest in the 

 regions of highest relief." 



These very general laws may be put into 

 more special forms that are directly proved 

 by the statistics : 



I. Mountainous regions are more un- 

 stable than plains. 



II. Sea-coasts near oceans that rapidly 

 deepen, especially such as are bordered by 

 high mountains, are more unstable than the 

 coasts of shallow seas, especially if such 

 coasts have no mountains near them. 



III. The shorter and steeper slopes of 

 mountain chains are the more unstable. 



* Relations entre le relief et la sismioite, ArcJdves 

 des Sciences Phys. et Nat., 1895 ; Le Japon sismique, 

 idid., 1897; Les Etats-unis sismiques, ibid., 1898 ; 

 Les Indes Neerlandaises sismiques, Nat. Tijd. der 

 Eon. Nat. Ver. in Nederhindsch — Indie, Dl. LVI., 

 1896 ; Etude critique des lois derepartion saisonniere 

 des s6ismes, 3Iem. de la Soc. " Alzate," tomo IV. ; 

 Eelation entre la frequence des tremblements de terre 

 et leur intensite. Bull. d. Soc. Sismologica Ital., Vol. 

 III. ; La peninsula iberioa seismioa y sur colonias, 

 Ann. de la Soc. EspaTiola de Hist. Nat.,\\iom.o XXIII. ; 

 Seismic Phenomena of the British Empire, Qaar. 

 Jour. Geol. Soc, Vol. LIL, 1896. 



