576 A. W. GRABAU LOWER ORDOVICIC FORMATIONS 



T. bryonoides Hall (T. serra) 

 T. fruticosus Hall 

 T. bigsbyi Hall 

 Didymograptus extensus Hall 

 D. Mfidus Hall 

 Caryocaris ivrightii Salter 

 Dictyonenia, Lingula, and Obolella. 



D. bifidus is an Upper Arenig type, but it is probable that this series 

 of rocks is Lower Arenig, as indicated by the other species. 



The Llandeilo is here represented by the Barr Series, which comprises" 

 the following members, in descending order : 



7. Benan conglomerate 1,000 feet plus 



Stinchar calcareous group: 



6. Green niudstones and shales with 



1. Didymograptus supertis Lapw. 



2. Dicellograptus sextans Hall 



3. Glathrograptus cuneiformis Lapw. 



4. Glossograptus hicksii Hopk. 



5. Gryptograptus tricornis Can*. 



6. Diplograptus rugosus Emm 30 feet 



5. Compact limestone with few fossils, including 



Saccamina and Girvanella. 



4. Nodular, flaggy Maclurea limestone and shales with 

 Haclurea logani, Tetradlum peachi, etcetera. Thick- 

 ness of 5 and 4 about 70 feet 



3. Orthis confinis beds, flaggy, impure, calcareous, with O. 

 conftnis Salter, 0. altemata (Salter), Strophomend 

 grandis (Salter) . Thickness 60 feet 



Kirkland group: 



2. Purple sandstones and grits, with occasional Orthis 



confinis and Strophomena 40 feet 



1. Purple conglomerate 150 feet plus 



The conglomerate rests on the eroded surface of the Lower Arenig and 

 consists of worn fragments of these rocks and the volcanics associated 

 with them. It contains pebbles of chert, black shale, lavas, and tuffs, 

 "together with serpentine, gabbro, dolomite, and even granite." 13 The 

 calcareous beds make correlation with other horizons possible. The flags 

 with Orthis confinis also contain O. calligramma (Dalm.) in some sec- 

 tions, together with O. flabellulum (Sow.) and Strophomena expansa 

 (Sow.). The first of these is wide-spread, occurring in the Baltic prov- 

 inces of Eussia in horizon B III and C (see postea). O. flabellulum is 



13 Peach and Home : Loc. cit., p. 484. 



