126 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
to give a brief statement on the major divisions of the early Middle Ordovician 
in the Antelope Valley west of Eureka, Nev., and in the range fronting French- 
man Flat about 45 miles northwest of Las Vegas, Nev. Although I have seen 
and collected from all the rocks mentioned herein, I am indebted to Drs. Edwin 
Kirk and C. W. Merriam, of the U. S. Geological Survey, for information as to 
localities and for the use of their collections. 
ANTELOPE VALLEY AND TOQUIMA RANGE 
Between the top of the Canadian and the base of the Upper Ordovician, in the 
region between Eureka and the Antelope Valley, occurs a remarkable thicken- 
ing of the sequence to the west. Examination of both sides of Antelope Valley 
and the east side of the Toquima Range, 25 miles west of the Antelope Range, 
is necessary to build a composite section. Even after this is done the complete 
section has never been ascertained, and some uncertainty exists as to sequence. 
In ascending order the following divisions were recognized : 
Poconip Group: With Orthidiella zone, Pallaseria (formerly Muitrospira) 
zone, Desmorthis zone, Anomalorthis zone, Rhysostrophia zone ; EUREKA GROUP: 
With a lower 25-foot sandstone, yellow limestone with Sowerbyites, dark shale 
with Reuschella, and upper or Eureka quartzite. All the zones below the lower 
sandstone have hitherto been placed in the Upper Pogonip limestone, a term 
that has for many years outlived its usefulness. 
Poconrp Group: Orthidiella zone.—Lowest zone of the sequence character- 
ized by the small brachiopod Orthidiella. Specimens abundant, often silicified. 
In Whiterock Canyon, Roberts Mountains Quadrangle, the limestone of the zone 
rests on green shale thought to be the same as that at the top of the Canadian. 
The Orthidiella zone is better developed and replete with fossils in the first ridge 
east of Frenchman Flat on the Las Vegas, Nev., Quadrangle. Here 150 feet of 
heavy-bedded limestone underlies the Palliseria (Mitrospira) beds. Most of the 
brachiopods listed below were taken from the Frenchman Flat locality, but many 
of them were seen also in Whiterock Canyon. 
Idiostrophia nuda Cooper O. longwelli Ulrich and Cooper 
Ingria cloudi Ulrich and Cooper Orthidiella sp. 1 
Liricamera nevadensis Cooper Porambonites sp. 3 
Orthambonites eucharis (Ulrich and Cooper) Trematorthis masoni Ulrich and Cooper 
Orthidiella carinata Ulrich and Cooper T. robusta Cooper 
O. costellata Cooper T. tenuis Cooper 
O. extensa Ulrich and Cooper 
Correlation—At present few of the genera listed above have been certainly 
identified in any North American deposits other than those of Nevada. Brachio- 
pods suggesting Orthidiella occur in the Table Head series of Newfoundland. 
Trematorthis lévisensis Ulrich and Cooper is known from the limestone No. 2 
boulder bed of the Lévis shale. This suggests a younger age for this bed than 
hitherto suspected. 
Pallaseria (Mitrospira) zone.—Consists of a great thickness of heavy- 
bedded limestone abounding in the snail that gives the zone its name, and also 
