UENERAL GEOLOGY 31 1 



There are no important creeks or rivers that flow through or rise within 

 it. Bitter creek, the largest waterway, passes to the southward of the 

 Leucite hills, but receives the drainage from Killpacker creek, which 

 rises near Boars tusk, and also from a few gulches along the southern side 

 of the Leucite hills and from the gulch heading at Fifteen-mile spring. 

 All of the remainder of the drainage from the Leucite area is to the east- 

 ward and is tributary to the Great Divide basin. 



The separate or detached exposures of the leucitic or their closely re- 

 lated rocks are now known to be twenty-two. They range from talus- 

 covered hills, isolated volcanic necks, and associated dikes, as in the 

 Boars tusk and Badgers teeth, to lava flows with cones, as in the case of 

 most of the exposures. Besides these we apparently have in the " Tables " 

 examples of intruded sheets at different horizons, and one dike has been 

 met at a distance from a volcanic neck. 



The mesas have in some cases been built up of demonstrably succes- 

 sive flows, and on top of these are the cones. The cones are generalh^ 

 formed of fragmental pumice or of very cellular scoria, but at least one 

 is a huge blister of solid lava. Observation of the last named led one 

 of us (.J. F. Kemp) to infer that the cones generall}'' were blisters,* but 

 subsequent study of the other cones proves that they are almost all 

 composed of fragmental rocks and are segments of older cinder cones, 

 whose major part has been removed by erosion. 



The Twenty-two Leucite Hills 



The twenty-two separate exposures are shown on the accompanying 

 map, from Avhich their relations may be seen at a glance. This map is 

 based on the one of the U. S. Land Office, but the locations have been 

 checked, by observations with a Brunton pocket transit, from cone to 

 cone or from one recognizable feature to another. The need of names 

 in order that we may distinguish the separate exposures in the descrip- 

 tions has led us to apply to those which, so far as we can learn, have 

 hitherto received none the names of geologists who have been concerned 

 in their study or have contributed in other important ways to the geol- 

 ogy of Wyoming. 



In our nomenclature we have sought to apply the name " mesa " where 

 the exposure is flat and like a table, even though it might have a cone 

 on it and thus suggest a butte, and even though it had been called a 

 butte before, as in the case of Orenda, Pilot, North Pilot, Steamboat, and 

 Black Rock, which are currently called buttes. Butte, of course, implies 

 a sharp or pointed elevation, and is not to be correctly used for these 



*Bull. Ge.ol. Soc. Am., vol. 8, p. 174. 



