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SCIENCE. 



[Vol. IV., No. 



pound of bromine for every barrel of salt — being 

 greater than anywhere else in the world. The in- 

 flammable, high-pressure gas accompanying the salt 

 brine, especially in the Waverley conglomerate or 

 Logan group, is largely employed as well in forcing 

 the brine to the surface as in evaporating it. A lively 

 discussion regarding the origin of petroleum fol- 

 lowed this paper; in the course of which both Pro- 

 fessor Newberry and Professor Orton held that it 

 owed its existence to the slow distillation of the 

 organic remains originally contained in the enclosing 

 shales, the 'sands' themselves being remarkably free 

 from organic remains, and acting merely as reser- 

 voirs. 



No paper presented to the section was greeted with 

 more interest or closer attention than that by Prof. 

 J. E. Hilgard, director of the U. S. coast-survey, on 

 the relative level of the Gulf of Mexico and the 

 Atlantic Ocean, with remarks on the Gulf Stream 

 and deep-sea temperatures. Inasmuch as we hope 

 soon to give this most valuable communication to the 

 readers of Science, only its two most essential points 

 need be mentioned here. These are: 1° The discov- 

 ery by a most careful series of levels, run from Sandy 

 Hook and the mouth of the Mississippi River to St. 

 Louis, that the Atlantic Ocean at the former point 

 is 40 inches lower than the Gulf of Mexico at the 

 latter point; and, 2° That ocean-water at all depths 

 exceeding one thousand fathoms possesses a temper- 

 ature of nearly 35° F., because this is the temperature 

 consistent with its greatest density. Should the 

 water become either cooler or warmer, it must ex- 

 pand; this it cannot do on account of the super- 

 incumbent pressure. 



Monday was the day which it was proposed, accord- 

 ing to the suggestion of the sectional committee, to 

 set apart for papers and discussions relating to the 

 crystalline rocks; but events seemed to demonstrate 

 the apparent impossibility of especially devoting any 

 fixed time to this or any other subject. It is to be 

 regretted that a more definite topical arrangement of 

 papers cannot be introduced into the programme by 

 the committee, and even more deeply is it to be de- 

 plored that what little trace of such an arrangement 

 may appear is entirely obliterated by the failure of 

 authors to respond when their papers are announced. 

 Surely a programme carefully arranged according to 

 subjects, and strictly adhered to, would do much to 

 expedite the discussions and increase the interest of 

 the whole section. 



The first paper read was one postponed from Friday 

 by Prof. E. W. Claypole, on some fish remains re- 

 cently discovered in the Silurian rocks of Pennsyl- 

 vania. Small fluted spines and oval shields were 

 exhibited closely resembling certain fish remains from 

 the Ludlow rocks of England, which for fifty years 

 past have been recognized as the oldest known traces 

 of vertebrate life on the globe. The studies of Hux- 

 ley and Lankester were quoted as proving the true 

 ichthyic character of these fossils; and the differ- 

 ences between the European and American speci- 

 mens, based on a microscopic examination, were 

 noted. The horizon in which the Pennsylvanian 



specimens were found was considerably below the 

 water-line group (equivalent to the lower Ludlow r of 

 England), so that we may safely conclude that these 

 are the oldest vertebrate remains yet discovered. 



Prof. A. S. Ewing then presented some calculations 

 regarding the rate of chemical erosion of Appalach- 

 ian limestones, based on observations in the Nittany 

 valley. These are interesting, but do not, as Mr. 

 Ashburner remarked, seem capable of any general 

 application, since erosion is so very unequal in differ- 

 ent areas. 



A general discussion upon the subject of maps 

 and map-making was introduced by Prof. George H. 

 Cook's admirable paper on the geological survey of 

 New Jersey. After giving a short account of the 

 work accomplished by the two earlier surveys of the 

 state, the results secured by the existing one, which 

 has been under its present management since its 

 organization in 1864, were recounted. A large geo- 

 logical wall-map of the entire state was produced in 

 1868, and there were exhibited the three completed 

 sheets of the new and much larger topographical 

 map (scale, a mile to an inch) now in progress. This 

 will finally contain seventeen sheets, and, to judge 

 from what has already appeared, will be a model of 

 accuracy and beauty. The necessity of devoting the 

 small annual appropriation almost exclusively to 

 topographical work has heretofore hindered the study 

 of the geology, but the recent assumption of the 

 former by the U. S. geological survey will now leave 

 this fund free for strictly geological investigations. 

 The practical use of the survey was illustrated in the 

 success of the artesian borings, advised by the state 

 geologist, on the Atlantic coast. 



Remarks on the New-Jersey maps were then made 

 by Mr. Trelawney Saunders, Major Powell, and oth- 

 ers. A preliminary geological wall-map of the United 

 States, colored as far as reliable data could be ob- 

 tained, together with another of the states of New 

 York, Pennsylvania, and New Jersey, compiled from 

 the work of Hall, Lesley, and Cook, was exhibited 

 by the U. S. geological survey, and discussed, at the 

 request of Major Powell, especially by those gentle- 

 men present who had aided in their compilation. 



Professor Henry S. Williams of Cornell university, 

 in a paper on the influence of geographical and 

 physical conditions in modifying fossil faunas, intro- 

 duced the exceedingly important subject of the 

 extent to which paleontological evidence is to be 

 regarded as an absolute guide in correlating strata in 

 different regions. This, as is well known, was the 

 subject of the address delivered before the geological 

 section of the British association in Montreal by its 

 president, Professor Blanford, and, as may readily be 

 imagined in view of the many eminent paleontolo- 

 gists present in Philadelphia, excited a lively discus- 

 sion, the interest in which continued until the final 

 adjournment of the section. Professor Williams ex- 

 plained a series of sections, principally in Chemung 

 and Catskill rocks, taken from a number of localities 

 across New- York state, and deduced from them abun- 

 dance of proof that faunas in Devonian times, as at 

 present, changed not only geologically in sequence 



