30 



SCIENCE. 



[N'. S. Vol. XXI. Xo. 523. 



tional support. One hundred more subscribers 

 in tliis country would probably encourage the 

 editors to go on with it. These ought not 

 to be difficult to get. To those who are un- 

 acquainted with it we may say that it is quite 

 unique and occupies a different and higher 

 plane than most bibliographic works. There 

 is not merely a more or less roughly classified 

 list of titles and brief abstracts of contents, 

 but a series of logically arranged critical re- 

 views pointing out the bearing of the paper, 

 reviewed on the state of knowledge of the sub- 

 ject. The systems of cross referencing and 

 indexing are wonderfully complete. The re- 

 views are arranged primarily into twenty 

 chapters, as follows : Cell, sex products and 

 fertilization, parthenogenesis, asexual repro- 

 duction, ontogenesis, teratogenesis, regenera- 

 tion, grafting, sex and pleomorphism, alterna- 

 tion of generations, latent characters, correla- 

 tion, death, general morphology and physiol- 

 ogy, heredity, variation, origin of species and 

 specific characters, geographic distribution, 

 nervous system and functions, general theories. 

 Most of these chapters are elaborately sub- 

 divided. A feature has been comprehensive 

 reports on the state of our knowledge of special 

 topics. No one who is interested in the de- 

 velopment of the- topics named above can 

 view with equanimity the prospect of the loss 

 of this review. It is to be hoped that every 

 biological laboratory and every library that 

 has a scientific department and which lacks 

 L'Annee hiologiqne will at once send a sub- 

 scription to Schleicher frei-es, Paris, the pub- 

 lishers, or to Professor Y. Delage, Sorbonne, 

 Paris, the chief editor. 



CiiAS. B. Davenport, 

 Jacques Loeb. 



THE epidiascope. 



To THE Editor of Science: Who saw the 

 epidiascope at the St. Louis Exposition? It 

 appears in the catalogue of German scientific 

 instruments at page 211, and is a most inter- 

 esting type of projection apparatus, of espe- 

 cial utility to all schools. The possibility of 

 speedy and facile transition from reflected to 

 transmitted light, if worked out to the last 

 optical and mechanical detail, would render 



it worthy of wide adoption. The diffusion of 

 knowledge of all the arts and sciences ought 

 to be very materially enhanced by this per- 

 fected apparatus. The projection of printed 

 pages, photographs, charts and works of art, 

 all without the necessity of photography, is 

 most important. The name of the inventor 

 is not given: presumably Carl Zeiss, of Jena. 



David P. Todd. 

 Amherst College Observatory. 



SPECIAL ARTICLES. 



THE influence OF CAVERNS ON TOPOGRAPHY. 



It is well known that caverns, particularly 

 those in regions underlain by limestone, are 

 frequently associated with depressions in the 

 surface above them, such as sink-holes, or 

 swallow-holes, as they are commonly termed. 

 It is also a familiar fact that the falling of 

 portions of the roofs of caverns sometimes 

 gives origin to ravines, canyons, etc., which 

 are occasionally- spanned by remnants of the 

 roofs which remain in place, as in the case of 

 the natural bridge of Virginia, and in other 

 similar ways influence surface relief. A char- 

 acteristic feature of this class of topographic 

 changes is that depressions in the surface of 

 the land are produced. The class of land 

 forms to which attention is here invited, how- 

 ever, are exceptional, and, as it seems, have 

 not been recognized as having a direct asso- 

 ciation with caverns, for the reason that they 

 stand in relief and in some instances are con- 

 spicuous and picturesque on account of their 

 height and boldness. 



The topography of most regions the world 

 over owes its leading characteristics, aside 

 from elevation above the sea, to erosion. The 

 chief exceptions are elevations produced by 

 volcanic and glacial deposition. Erosion, par- 

 ticularly by streams, leads to the production 

 of two classes of earth features, one class be- 

 ing due to the removal of material, as in the 

 excavation of valleys, while the other class 

 includes the remnants of uplands left when 

 eiosion to a plane surface is incomplete. In 

 the production of such topographic changes, 

 weak rocks, as a rule, are removed most readily 

 and are replaced by depressions; while resist- 

 ant rocks persist longer and are left in relief. 



