712 



SCIENCE 



[N. S. Vol. XLIII. No. 1116 



fessor of vertebrate paleontology. He will re- 

 tain his position at the American Museum of 

 ISTatural History. 



Professor Ernst Gaupp, of Konigsberg, 

 has accepted a call to the chair of anatomy at 

 Breslau. 



leaves are abundant in the accompanying 



DISCUSSION AND CORRESPONDENCE 



AGE OF THE TtJXPAM BEDS 



In Science of February 10, 1911, the writer 

 gave a preliminary sketch of the Tertiary de- 

 posits of northeastern Mexico. In this com- 

 munication the beds occurring in the vicinity 

 of Tuxpam with their wealth of fossils, which 

 appeared to be largely new or undescribed 

 species, were stated to probably belong to the 

 Miocene, and this reference has been followed 

 in later publications both by himself and by 

 others. 



While both gasteropods and bivalves were 

 abundant at this locality, the most character- 

 istic fossils of these beds were the echino- 

 derms, which included great numbers of a very 

 large Clypeaster, one or more species of Schi- 

 zoduSj Macropneustes and Cidaris. None of 

 these special forms were reported by other ob- 

 servers from the region to the south of Teco- 

 lutla, but the similarity of the deposits of the 

 lower coastal area seemed to indicate their 

 continuity, and since such fossils as had been 

 described from these continuations were con- 

 sidered of Miocene or Pliocene age, it seemed 

 probable that the Tuxpam beds were also of 

 that age. 



During the examinations made in the 

 coastal area between Tuxpam and Tampico 

 since this publication, numerous collections of 

 fossils have been made and these are now being 

 examined. We find that the Tuxpam 

 Clypeaster, Cidaris and Macropneustes occur 

 elsewhere in connection with the nmnmulites, 

 cristillaria and orbitoides of the Oligocene, but 

 where we find this association we do not find 

 the large number of gasteropods and bivalves 

 which are found at Tuxpam, or on the San 

 Fernando. The shells usually accompanying 

 these echinoderms around Tampico are simply 

 a small pecten, a nucula, and one or two small 

 gasteropods. In some localities imprints of 



Such an association of fossils seems to re- 

 quire the reference of the Tuxpam beds to the 

 Oligocene, and if this be true, it would ap- 

 pear that along the western gulf shore there is 

 no marine Miocene on the surface between 

 Tirxpam and Galveston. E. T. Bumble 



NITER SPOTS 



To THE Editor op Science : In a recent nimi- 

 ber of Science^ is to be found an article by 

 Saekett and Isham relating to the formation 

 of " niter spots " in the arid regions of the 

 western United States. In a more recent 

 number of the same magazine^ Stewart and 

 Peterson have given a lengthy and interesting 

 discussion of this paper and also a descrip- 

 tion of these brown spots. These later writers 

 have attributed the origin of these nitrates to 

 the leaching and concentrating action of irri- 

 gating water upon the nitrates occurring in 

 the shales and sandstones (or country rock) 

 adjacent to and miderneath the affected areas 

 from which the soil has been derived. Their 

 field observations were in Utah, where they de- 

 scribe the appearance of brown " niter spots " 

 in certain irrigated fields. 



While making some geological investiga- 

 tions in northwestern Nevada in 1912 it was 

 the present writer's pleasure to make some 

 notes relating to brown " niter spots " occur- 

 ring on the playas. The observations being in 

 strict conformity with well-known principles 

 of commercial niter formation, the necessity 

 of much speculation before arriving at a con- 

 clusion as to their origin was obviated. It is 

 trusted that the few simple facts recorded at 

 that time will serve in giving some added 

 light on the subject in hand. 



In traversing the playas brown spots were 

 frequently noted on the surface in connection 

 with alkali salts. When the brown mixtures of 

 earth and salts were tested they invariably 

 showed large amounts of nitrates. In places 

 on the surface where the brown color was not 

 present no nitrates were noted. Pits dug 

 failed to show nitrates at greater depths than 



1 N. S., Vol. XLII., p. 452. 



2 N. S., Vol. XLIII., pp. 20-24. 



