512 



SCIENCE. 



[Vol. I., No. 18. 



parts may be distinguished, — one vertical, descend- 

 ing from the blastopore; the other horizontal, run- 

 ning forwards. In the dorsal wall of the latter, the 

 chorda dorsalis makes its first appearance. The 

 canal closes at the same time as the medullary tube. 

 Just before the closure of the blastopore, the ' aniage ' 

 of the medullary cord extends around it. After 

 the external closure, the communication between 

 the medullary tube and the digestive cavity is still 

 maintained by the canal. Strahl uses the unfortu- 

 nate term ' medullary cord ' to designate the medul- 

 lary tube, notochord, and part of the primitive streak 

 together: hence he describes the chorda as being 

 diflerentiated from the medullary cord. This only 

 adds to the confusion, and is the more to be re- 

 gretted, since the real origin as described by him 

 agrees with the accounts of other writers, — it is at 

 first a modification of the epithelium of the neuren- 

 teric canal. The middle portion of the chorda is the 

 first to be grown over by the entoderm : therefore the 

 two ends remain longer uncovered than the middle. 

 /it the time when the peripheral mesoderm, form- 

 ing the area vasculosa, reaches the germ-wall, the 

 latter is already completely fissured. Blood-vessels 

 have begun to appear before this time, and without 

 the participation of the germ-wall. C. S. Minot. 



THE INTERNATIONAL GEOLOGICAL 

 CONGRESS. * 



The compte rendu of the second session of this 

 congress, held at Bologna last year, has just appeared 

 in a thick octavo, with abundant illustrations. The 

 history of the congress, forming the first part of the 

 volume, was prepared by the president, Capellini, 

 and consists of a brief account of its origin with the 

 meeting of the American association for the advance- 

 ment of science in 1876, a summary of the results of 

 the first meeting at Paris in 1878, a list of the mem- 

 bers and officers of the first congress, an account of 

 the choice of Bologna as the rendezvous for the sec- 

 ond meeting, of the nomination of the international 

 commissions, of the organization of the second con- 

 gress, with its rules and regulations, and lists of the 

 members, delegates, and officers. In connection with 

 this latter portion, it is curious to note that a number 

 of the more eminent geologists who originally took 

 part in it no longer belong to the congress; and also 

 that the number of Italians at the congress was 202, 

 although the geological society of Italy has only 120 

 members, of whom 14 are foreigners. 



The second part, prepared by Delaire and Fontan- 

 nes, besides the proceedings at the different sittings, 

 contains a number of appendices on geological color- 

 ing and nomenclature, and one on the classification 

 of mineral masses by M. de Chancourtois, accompa- 

 nied by a tabular view of lithological synthesis. This 

 author objects to the indiscriminate use of the word 

 'rock,' and proposes instead the word 'lithe,' which 

 he subdivides, according to the origin of the rock, 

 into analithes, endo-analithes or endolithes, exo- 

 analithes or exolithes, catalithes, peri-catalithes or 

 perilithes, apo-catalilhes or apolithes. The reports 

 of the discu>sion are interesting, as showing the ex- 

 treme difficulty of reaching any unity in classifica- 

 tions, even on the most trifling points. 



The third part (documents of the congress, pre- 

 pared by the same hands) contains a brief description 

 of the collections and maps exhibited at the congress. 

 Among these may be mentioned the geological map 

 of Italy (scale, , „, ,„ ), engraved in the colors of the 

 international commission, especially for the congress, 



in two editions, — one with the mountains figured in 

 hachures, and the other without them. The latter 

 is the clearer, and preferable as a geological map. 

 It is curious that a map on a scale so small should 

 have twelve colors devoted to crystalline rocks, and 

 only ten to the sedimentary strata; and it answers 

 well its purpose as a study of geological map-coloring. 

 The Italian committee also prepared a geological 

 and paleontological bibliography of Italy, containing 

 mention of 6,506 memoirs from the days of Aelianus 

 (693 B.C.) to 1881. Its arrangement is remarkably 

 clear and simple. 



The fourth part (annexes) contains in extenso, and 

 in their original language, the reports sent by the 

 national committees to the international commissions 

 established in 1878. They are followed by summaries 

 of a few individual reports on the unification of 

 nomenclature, or of graphic processes. 



The scientific communications are the following: 

 1°. Macrographical classification of the trachytes of 

 Hungary, by J. Szabo, already mentioned in Science. 

 2°. On the classification of the ancient stratified rocks 

 of the island of Sardinia, by J. G. Bornemaun, who 

 has found a number of primordial fossils, paradox- 

 ides, etc., with intercalation of the second fauna. 

 This would seem to be analogous to the condition 

 of the Taconic of Vermont. 3"^. On the cretaceous 

 system and the great sand-dunes of the northern 

 Sahara, by G-. Roland. He considers the cretaceous 

 as consisting of the middle and upper divisions ; that 

 the sand-dunes constitute distinct chains, formed 

 entirely by the wind, and depending for their orog- 

 raphy on topographical accidents; that the larger 

 dunes are not moved by the action of the wind, the 

 position of the masses, and the orography of the 

 chains, varying but little, excepting that, as a mass, 

 they are very slowly travelling toward the south-east, 

 and the quantity of sand is continually increasing. 

 4°. Memoir on the geology of New South Wales, by 

 C. S. Wilkinson, who recognizes all the great divis- 

 ions, from the Silurian to the tertiary inclusive, and 

 confirms the truth of the report of the late Rev. W. B. 

 Clarke of the association of triassic plants with the 

 marine carboniferous fauna. 



Next follows an account of the three excursions 

 taken by the congress to Florence, Pisa, and Carrara. 

 Accompanying the latter is a section from Carrara to 

 the central region of the Alpi Apuane, in which the 

 Carrara marbles are shown to be of triassic age; 

 fossils of this age being found in, above, and below 

 them. 



We next have the prize memoirs on the unification 

 of graphic processes in geological maps. The best was 

 considered to be that by A. Helm; next comes the 

 one by A. Karpinsky, and, lastly, that by M. Maillard. 

 Mr. Helm's memoir contains a plate exhibiting the 

 application of his system to profile sections, which is 

 very clear and plain. 



"The last or fourth part contains numerous reports 

 on geological nomenclature and coloring of more or 

 less importance. It does not seem to have occurred 

 to the congress to compare the different methods in 

 actual use by the different geological surveys. None 

 of the different reports seems to give these, except 

 that by Major J. W. Powell of the U. S. geological 

 survey. The difficulty, with our still imperfect 

 knowledge of geology, of establishing any system of 

 universal application, seems very great, and is well 

 illustrated by Professor Hubert when he expressed 

 the ingenious wish that votes should only be taken 

 on those points on which all are agreed. 



In conclusion, we may mention the very sensible 

 motion of Mr. Torel, that the congress, while leav- 



