June 23, 1911] 



SCIENCE 



971 



Pholadomya sp. 



Cardium congestum Con. 



Buccinopsis parryi Con. 



Rostellaria? (VolutomorpJia) texana Con. 



Pugnellus sp. Etc. 

 Xas Isletas : 



Sphenodiscus pleurisepta Con. 



Mactra texana Con. 



Cardium congestum Con. 



Turrit ella sp. Etc. 

 Arroyo Toro Colorado, 1 m. below Las Isletas : 



Sphenodiscus pleurisepta Con. 



Nautilus deLayii? 



Ostrea sp. 



Mactra texana Con. 



Crassatella sp. 



Cardium coniiestum. 



Breviarca sp. 



Buccinopsis parryi Con. 



Pugnellus sp. 



Natica collina Con. 



Natica texana Con. 



Rostellaria? (Volutomorpha) texana Con. 

 Etc. 



This locality also furnishes a number of 

 specimens of crabs. 



A selection of specimens representing sev- 

 eral of the species under discussion, together 

 ■with a number of others occurring in the same 

 heds, were submitted to Dr. T. W. Stanton, of 

 the United States National Museum, and my 

 identifications of the Conrad forms were con- 

 firmed by Dr. L. W. Stephenson, who states 

 that the Rostellaria? of Conrad is a Voluto- 

 morpha. 



Major Emory, in the first part of the Boun- 

 dary Survey report, on page 68, gives a de- 

 scription of Las Isletas and the falls of the 

 Eio Grande with a full-page illustration op- 

 posite. This description would indicate that 

 the falls of the Eio Grande and Las Isletas 

 "were the same. The truth is that Las Isletas 

 is located about the mouth of Castano Creek, 

 "while the falls are some four miles lower down 

 the river just below the mouth of Caballero 

 Creek. 



It will thus be seen that our collections were 

 made from localities directly on the line of 

 travel of the Boundary Survey party and it 



seems highly probable that the original speci- 

 mens described by Mr. Conrad were in reality 

 obtained from these same beds. 



The horizon is the uppermost portion of our 

 Escondido beds. The fossils are among the 

 latest Cretaceous forms of which we have any 

 present knowledge in this region. 



The Cretaceous-Eocene contact is well 

 shown three miles below Toro Colorado, just 

 above the falls of the Rio Grande and on 

 Caballero Creek. 



The only other records I can find of any of 

 these forms are as follows : 



Professor G. D. Harris, in " The Tertiary 

 Geology of Southern Arkansas," gives a list 

 of fossils collected by Dr. C. A. White in 1887 

 at his camp eighteen miles southeast of Eagle 

 Pass, Texas, which were supposed to be basal 

 Tertiary. Among these there is a cardium 

 which Mr. Harris figures both in this paper 

 and later with his Midway fauna " Bulletin of 

 American Paleontology, No. 4," without giving 

 it a specific name. 



This camp was probably at the Eagle Pass- 

 Laredo road crossing near the junction of 

 Cuevas and Pena creeks and on or near the 

 Cretaceous-Tertiary contact. The cardium is 

 unquestionably the Cardium, congestum of 

 Conrad, while the other forms named by Pro- 

 fessor Harris are from the overlying Midway. 



Mr. T. W. Vaughan in his Report on the 

 Rio Grande Coal Fields of Texas gives a list 

 of fossils collected 18J miles southeast of 

 Eagle Pass. This must also have been in the 

 same vicinity. His list contains a form 

 identified as " Mactra cf. mooreana " which, in 

 view of our later discovery, may be more 

 properly called Mactra texana, and Cardium 

 cf. eufalense may be Cardiiim congestum. 

 E. T. Humble 



BACTERIOLOGICAL METHODS FOR THE ESTIMATION 

 OP SOIL ACIDITY 



The general prevalence of acidity in the 

 older soils of the United States has been the 

 cause of increasing comment, within the past 

 few years. It is well known that the tendency 

 of cultivated soils to become acid is intensified 

 by the use of commercial fertilizers, and, gen- 



