373 



In regard to the discordance in the results at which these eminent 

 conchologists have arrived, it may arise not only from the unequal 

 opportunities which they have enjoyed of examining the necessary 

 data, but also, in part, to the different estimate which they have 

 formed of the amount of variation necessary to constitute a distinct 

 species. One example will sufficiently illustrate my meaning. Those 

 naturalists who agree with M. Deshayes in referring all the living 

 varieties of Lucina divaricata brought from different countries to 

 one and the same species, will identify many more fossils with re- 

 cent shells than those who agree with Dr. Beck in dividing the 

 same recent individuals of Lucina divaricata into six or eight di- 

 stinct species. Provided, however, each zoologist is consistent 

 with himself, and provided the distinctive characters relied on as 

 specific by each are commensurate one with another, no confusion 

 will arise. 



In reviewing the proceedings of the Society during the last year, 

 I find that the remaining memoirs, numerous as they are, may be 

 all referred to one great class of subjects, for they either relate to 

 changes now going on upon the surface of the earth as attested by 

 man, or to geological proofs of similar changes since the rivers, lakes, 

 and seas were inhabited by the existing species of testacea. Under 

 these heads I shall be led to consider the effects of modern earth- 

 quakes in upheaving and depressing the land ; the gradual rising of 

 land in one region and the lowering of its level in another ; the rolling 

 in of great waves of the sea upon the coast during earthquakes ; the 

 transportation of rocks by floating ice ; the signs of upraised beaches 

 containing marine shells ; erratic blocks ; alluvial deposits of different 

 ages; and other kindred topics on which a variety of new facts have 

 been collected. 



The last year has been signalized in South America by one of 

 those terrific convulsions which have so often desolated the western 

 coast since the discovery of the new world. A brief notice of this 

 catastrophe was sent me by Mr. Alison, written immediately after 

 the event. He mentions that on the 20th of February, 1835, when 

 Conception, Chilian, and other towns were thrown down in ruins, 

 the sea first retired from the shores of the Bay of Conception, and 

 then returning in a wave about twenty feet high, rolled over several 

 of the towns, and completely destroyed whatever the earthquake 

 had left uninjured. He also states that the coast of the bay was 

 reported to have been heaved up, and that a rock off the landing- 

 place at the port of Talcahuano, which before the shock was nearly 

 level with high water, stood afterwards three feet above that mark. 

 Large fissures were made in the earth, and water burst from some 

 of them. 



In these and other particulars Mr. Alison's letter agrees with 

 the more circumstantial account sent to the Royal Society by 

 Mr. Caldcleugh, who was resident at Valparaiso, but who drew his 

 information in great part from eye-witnesses. He mentions that a 

 great number of the volcanos of the Chilian Andes were in a state 

 of unusual activity during the shocks, and for some time preceding 



