March 6, 1885.] 



SCIENCE. 



191 



est in it is increasing, however, may be judged 

 from the number of American students who 

 have been and still are pursuing it at various 

 German universities. What is needed in this 

 country are well-equipped petrographical labo- 

 ratories, so that those who are unable to 

 avail themselves of the facilities which Europe 

 affords may not be compelled to remain in 

 ignorance of what is daily becoming a more 

 and more necessary part of a geologist's train- 

 ing. An attempt to organize such a laboratory- 

 has recently been made at the Johns Hopkins 

 university and the encouragement which it 

 has alread}* received seems to abundantly jus- 

 tify the experiment. 



Heretofore microscopical petrography has 

 been essentially a branch of mineralog\ T , but 

 its future certainty lies in the far wider sphere 

 of geolog}\ The mere laboratory study of 

 isolated rock-specimens, which has served so 

 good a purpose in the perfecting of delicate 

 and accurate methods, no longer possesses any 

 significance, now that these are so thoroughly 

 developed. What in Germany has been secured 

 by years of patient labor may now be learned 

 in a comparatively short time. Geologists have 

 only to know and realize its application to their 

 field of w^ork, in order to eagerly avail them- 

 selves of such an important aid. The use of 

 the microscope alone will in future produce but 

 little that is new ; but its possibilities in geol- 

 og}', when intelligently empkryed in connection 

 with the most detailed and careful field-work, 

 -—the necessity of which has been increased, 

 not diminished, by its introduction, — cannot 

 be easily overrated. 



What paleontology has done for the fossilifer- 

 ous deposits, this, and even more, the micro- 

 scope must do for the crystalline rocks. The 

 less altered forms of igneous masses have thus 

 far been almost exclusively studied ; and, 

 although they still have much to teach us, it is 

 not by their investigation that the microscope 

 is destined to yield its greatest assistance to 

 geology. The changes, structural and chemi- 

 cal, which go on in rocks after they are first 

 formed, leave behind them more or less distinct 

 traces which it is the special province of the 

 microscope to follow out and interpret. Of 

 how much has alread} 7 been learned regarding 

 the alteration of sedimentary rocks near their 

 contact with eruptive masses, the work of 

 TCosenbusch in the Vosges Mountains, of Lossen 

 in the Hartz, and of Hawes in New Hamp- 

 shire, is abundant proof. The wide-spread 

 changes which rocks subjected to regional 

 metamorphism have undergone, are far more 

 complicated and difficult, but they can un- 



doubtedly be studied with as great success. 

 It is by dealing with such problems as Lossen, 

 Renard, and Lehmann, in Europe, and Wads- 

 worth in this country, have especially pointed 

 out, that the microscope in geology can in 

 future render its best service. The manner 

 in which this can be accomplished is by the 

 patient following, step by step, of unchanged 

 rocks into their most completely altered equiv- 

 alents, and carefully comparing the condition 

 of each constituent at every point. In this 

 manner the succession of changes which they 

 undergo may be as completely worked out as 

 though we could see the process actually going 

 on before our eyes. The alterations of olivine 

 and enstatite to serpentine, of p}Toxene to 

 hornblende, and even the reaction of two 

 minerals upon each other in forming a third 

 of intermediate composition, as shown in the 

 rim of amphibole which surrounds olivine 

 where it is in contact with plagioclase, have 

 all been traced by the microscope through 

 every stage. More recently the effects of 

 pressure exhibited by the bending and break- 

 ing of cr} T stals, the disturbing of their opti- 

 cal characters, and the local crushing of the 

 rock constituents, have been carefully studied. 

 This is found almost always to be attended b}~ 

 the formation of new minerals, like albite, zoi- 

 site, mica, garnet, etc., whose 3'ounger origin 

 is only to be proved by a microscopic investiga- 

 tion. It is impossible to mention here a tithe 

 of what has already been done in this direc- 

 tion, although a beginning has hardly 3-et been 

 made. What are especialty to be desired are 

 detailed studies of many small areas, where the 

 same rock, whether eruptive or sedimentar}', 

 can be traced from its original form to its most 

 altered state, and a comparison of the results 

 obtained in each. This Lossen 1 has recently 

 attempted for the southern Hartz, and has 

 thereby indicated what is perhaps the most 

 promising field for microscopic work in geol- 

 ogy. George H. Williams. 



THE SPANISH EARTHQUAKES. 2 



The Spanish peninsula has been the scene 

 of a series of earthquakes, which, for extended 

 duration and disastrous effects, surpasses any 

 thing that has been felt in that region in recent 



1 Studien an metamorphischen eruptiv- and sedimentgestein- 

 en, erlautert an mikroskopischi'ii bildern. Jabrbuch der preuss. 

 landesanstalt flir 1883, p. 619. 



2 In preparing this notice, the following journals have been 

 consulted; viz., Cronicacientifica (Barcelona), Science et nature, 

 La Nature, L'Astronomie, Comptes rendus, Cosmos, Hansa, Na- 

 ture, and various English and American newspapers. 



