rjQ GEOLOGY OF THE EUEEKA DISTRICT. 



litlioloo-ically, which present much the same aspect at each place, with a 

 similar Lower Devonian fauna, many of the forms being specifically 

 identical. The evidence goes to show that they belong essentially to the 

 same horizon, although the estimated vertical distance of the beds above 

 the Eureka quartzite varies considerably in the different localities. This 

 difference is undoubtedly due in part to the varying thickness of the under- 

 lying Lone ]\Iountain beds resting on the quartzite and partly to the more 

 rapid chano-es in some places than in others in the nature of the sedi- 

 mentation. In certain localities, under favorable conditions, the cal- 

 careous shale seems to have been deposited earlier than elsewhere. In 

 other words, the shale belts are not absolutely synchronous; in some places 

 they are known to be wanting. They may be taken as representing char- 

 acteristic horizons in the Lower Devonian without at the same time occu- 

 pying a sufficiently definite position to be made a datum point in deter- 

 minino- the thickness of the strata between the shale belt and the basal 

 member of the epoch. 



The following list includes all. species obtained from the calcareous 

 shale belts of Brush Peak, Atrypa Peak, and Combs Mountain. The 

 numerals affixed opposite the name of each species indicate from which of 

 the three localities they have been obtained. In this way it will be seen 

 at a glance which forms are common to more than one of these typical 

 localities. 



- - 3 Stromatopora. - 2 - Strophodonta demissa. 



- 2 - Favosites basaltica. - 2 3 Strophodonta inequiradiata. 

 1-3 Favosites n. sp. - 2 3 StrojAodonta perplaua. 



- - 3 Pacbyphyllum woodmani. - 2 - Strophodonta pnuctilifera. 



- 2 3 Zaphrentis. 1 2 - Ghonetes deflecta. 



- 2 - Lingula whitei. - 2 3 Ghonetes fihstriata. 



1 2 - Orthis impressa. 1 - - Ghonetes granulifera. 



12 3 Streptorhynchns chemungen- 1 - - Ghonetes hemispherica. 

 gis_ 1 2 - Ghonetes maerostriata. 



- 2 3 Streptorhynchns chemungen- - 2 - Productus navicellus. 



sis, var. pandora. - 2 - Productns subaciileatas. 



- 2 - Streptorhynchns chemungen- - 2 - Productus truncata. 



sis, var. perversa. 12 3 Spirifera piuonensis. 



1-3 Strophodonta calvini. - 2 - Spirifera undifera. 



