AGE OF THE ARAPAHOE AND DENVER. 221 



of Mr. Weed, largely owing to the same error which was committed in the 

 Denver fUld, namely, of grouping together as one flora the plants from 

 the coal horizon in the Laramie and those from a somewhat higher horizon 

 in what now prove to be Livingston strata. As the "Laramie flora" of 

 1N77, when these plants were determined by Lesquereux, consisted very 

 largely of the Denver plants from Table Mountain, it is natural that the 

 fossil plants of the two horizons in the Bozeman field should have seemed 

 to belong together. 



The Livingston formation is about 7,000 feet in thickness and is over- 

 lain by the Fort Union beds. Its lithologic character is almost identical 



with that of the Denver beds, the sandstones, conglomerates, and tuffs 

 consisting chiefly of andesitic debris of greal variety. In consequence the 

 strata are dark-brown or yellowish-brown in color, and contrast distinctly 

 with the quartzose sandstones of the Laramie with which they had been 

 previously classed. 



Mr. Weed and Mr. Peale both found the Livingston heds transgressing 

 the upturned edges of the underlying Mesozoic, although in less marked 

 degree than is the case for the Middle Park beds of Colorado. 



The fossil floras of the Bozeman coal beds and of the Livingston 

 beds have been carefully revised by Mr. Knowlton, with the result that a 

 marked difference appears between them. The Livingston flora contains 

 '_".» species, of which "_ , "_' have a known distribution in other places; 12 of 

 them occur in the Denver flora, 6 in the underlying Bozeman coal horizon, 

 or in other undoubted Laramie beds, and 4 in the Fort Union. This shows 

 a strong affinity with the Denver and a less marked alliance with the 

 Laramie and Fort Union floras. 



No vertebrate fossils have as yet been discovered in the Livingston 

 beds, but two horizons within the division called the "leaf beds" by Mr. 

 AVeed have yielded invertebrates. At one of' these horizons a few fresh- 

 water forms, including Goniobasis tenuicarinata, were found, all having a 

 resemblance to species known in the Fort Union beds. The species named 

 occur also in the Denver beds. The other invertebrate fauna consists 

 of brackish-water forms, viz: Ostrea subtrigonalis, Corbicula cytheriformis, 

 Corbula swbtrigonalis, and C. stibtrigonalis var. perundata. These forms occur 



