262 STANTON 



graphic relations of the various paleontologic zones are easily deter- 

 mined. 



In T. 6 N., R. 16 E., the gray beds forming the "upper part of the 

 Laramie" of Stone's classification have at least the maximum thick- 

 ness he assigns to them (2400 feet) as they underlie a belt considerably 

 more than a mile wide with a dip of 23°. Except near the base where 

 dinosaur remains are common, as already noted, fossils are rare in 

 this part of the section. In the upper half a few localities farther 

 west in the general region have yielded two or three species of Unio, 

 a Viviparus, and Campeloma muUilineata, but nothing distinctive. 

 Dinosaurs may range to the top of these "gray beds" but all the evi- 

 dence now available on their upper limit are in the following excerpts 

 from letters of Mr. Silberling: 



Dinosaur bones in top of Fox Hills and in base of Laramie [the 

 thickness of which be estimates to be 3000 feet]. Dinosaur bone 

 found in 1902 by myself 1800 or 2000 feet above base of [Laramie] 

 beds, but there is some doubt as to the bones being in position. 

 Dinosaur bones found in December 1908 within 600 feet of the top of 

 the formation by A. Strand. I have not as yet seen the locality. 



Under date of January 28, 1909, Mr. Silberling writes: 



Don't be surprised if I should drop you a line some of these days and 

 tell you John Winsbrough had found dinosaur bones in my Fort Union 

 No. I. He has found a big limb bone over in T. 4 N., R. 16 E., some- 

 where, but cannot at present locate it. 



Silberling's "Laramie" has the same limits as those given in Stone's 

 description, and his "Fort Union" begins with the "somber-colored 

 sandstone and shale which may represent the Livingston" according 

 to Stone. 



Mr. Silberling was employed in this area for several months last 

 year under my direction in collecting vertebrate and other fossils 

 for the U. S. Geological Survey and the U. S. National Museum. 

 He obtained an excellent collection of primitive mammals now being 

 studied by Mr. J. W. Gidley, who states that they are related to the 

 Puerco and Torrejon faunas of New Mexico with rather closer resem- 

 blance to the Torrejon. In order to indicate the relative positions 

 of his collections Silberling made use of prominent lithologic and 

 topographic features to separate the rocks into three members which 



