S16 



SCIENCE 



[ISr. S. Vol. XXVII. No. 



Here we are brought face to face with 

 the question: How far is it really worth 

 while to go in the establishment of the 

 formula? The geodesist contents himself 

 with the determination of at most two con- 

 stants for the figure of the earth. No one, 

 to my knowledge, has succeeded in estab- 

 lishing a formula which represents the 

 actual shape of the earth and exhibits at 

 least the most marked of the earth's mani- 

 fest irregularities of surface. Professor 

 Love, I believe, has established a formula 

 representing the irregularities of the first, 

 second and third degi'ees, but has not 

 deemed it worth while to go beyond this 

 extent. And so it would appear to me 

 that the time has come to halt in the estab- 

 lishment of a complex formula involving 

 forty-eight unknowns or more which at 

 the very best can give but an inadequate 

 representation of the actual facts of the 

 earth's magnetism. It would seem more 

 logical to stop with a 'certain finite number 

 of terms involving a limited number of 

 unknowns which represent, from a physical 

 standpoint, the chief and principal facts 

 of the magnetic condition of the earth. 

 The magnetization resulting from this 

 limited expression we should call our 

 "normal field," or "field of references" as 

 the geodesist calls his adopted figure, the 

 spheroid of reference. The residuals from 

 this field of reference would then receive 

 separate or special treatment in accordance 

 with their extent and their character. In 

 conclusion an application of this mode of 

 treatment to the United States was shown 

 (Slide 6). L. A. Bauee 



The Carnegie Institution of Washington 



SCIENTIFIC BOOKS 

 Revision of the Pelycosauria of North 



America. By E. 0. Case. Publication No. 



55 of the Carnegie Institution, Washington, 



July, 1907. 



This important monograph deals with the 

 most remarkable group of the Permian verte- 



brata. The Pelycosauria, popularly known 

 as " fin-back lizards," have been known 

 hitherto only from brief and scattered descrip- 

 tions principally by the late Professor Cope, 

 mostly based upon very incomplete material. 

 Dr. Case's studies of the last few years, aided 

 by a grant from the Carnegie Institution, have 

 done a great deal towards clearing up our 

 understanding of the structure and relation- 

 ships of the order. In the present memoir he 

 has brought together all the earlier descrip- 

 tions, and has redescribed and fully illus- 

 trated all the better-known types from the 

 more complete material now available. 



The rich and varied vertebrate fauna of 

 the Permian beds of northern Texas and the 

 adjacent parts of Oklahoma was first made 

 known to science by Cope in 187S and suc- 

 ceeding years. The collections upon which 

 his earlier descriptions were based were ob- 

 tained for him by Jacob Boll and J. C. Isaac 

 in 1878-80, and by Professor W. P. Cummins, 

 the well-known Texas geologist, in 1881-4. 

 In 1895-7 Professor Cope's collections were 

 greatly increased by the energy of the in- 

 defatigable collector, Charles H. Sternberg. 

 All these collections are now in the American 

 Museum of Natural History, along with addi- 

 tional material since obtained by Mr. Stern- 

 berg and Dr. Case. Dr. Case has also made 

 considerable collections for the University of 

 Chicago, and the Paleontological Museum of 

 Munich has acquired a large and valuable 

 collection through the exertions of Mr. Stern- 

 berg. So far as the reviewer is aware, there 

 are no important collections of vertebrates 

 from the Texas Permian, except in the three 

 institutions named. The preparation of the 

 specimens for study or exhibition is excep- 

 tionally difficult and tedious, since the bones 

 are visually encased in a hard flinty concretion 

 which can be removed only by laborious and 

 painstaking chipping. The progress of our 

 knowledge of this wonderful fauna is greatly 

 hindered by this difficulty in preparation. 



The vertebrate fauna of the Texas Permian 

 consists chiefly of armored amphibians 

 (Stegoeephalia), large and small, and primi- 

 tive reptiles of several groups. Its prime in- 

 terest lies in the fact of its great antiquity. 



