42 BULLETIN 77, ITIsriTED STATES NATIONAL, MUSEUM. 



Possibly future researches will reveal localities where the Glauco- 

 nite sandstone and overlying strata rest upon rocks younger than 

 the Dictyonema beds, which may be correlated with the American 

 Chazyan, and thus afford physical as well as faunal proof of the age 

 of the Kussian beds. 



It is of course possible that the lower part of the Russian section 

 succeeding the Dictyonema shale should be correlated with the 

 American Chazyan. The Russian faunas from Bl to the upper part 

 of Fl are remarkably uniform in character, changing only with the 

 introduction of new species. They seem to have developed almost 

 continuously, the few breaks in the sequence being of minor impor- 

 tance. As these faunas are limited to northern areas, their center of 

 origin and dispersal was undoubtedly the Arctic Ocean, from which 

 they invaded whenever opportunity offered. It is perhaps impossible, 

 as yet, to fix the date of their origin, consequently we can not prove 

 that they did not tenant the Arctic Ocean and possibly invaded the 

 Baltic Basin as early as Chazyan time. Nor is it improbable that 

 they continued existence in these northern provinces even to the 

 close of the Ordovician. However, in the absence of definite evi- 

 dence tending toward such conclusions we are obliged provisionally 

 to rely on faunal similarity with the standardized American sequence 

 in determining the relative ages of the Russia Ordovician formations. 



Respecting the upper part of the Baltic section, comprising the 

 upper Lyckholm and Borkholm, the range of possible error in corre- 

 lation with American deposits is much narrower and the problem on 

 the whole much less involved. As shown on page 35, the highly 

 characteristic Borkholm coral fauna is well developed in Arctic 

 America. Here it follows immediately on beds containing faunas 

 comparable with those found in Russia in a similar position with 

 respect to the upper Lyckholm and Borkholm. It was also shown 

 that these lower beds are strictly equivalent and presumably con- 

 temporaneous with the Black River and early Trenton formations in 

 the upper Mississippi Valley. As the middle Ordovician position of 

 these American strata is unquestionably established, a similar assign- 

 ment of their Russian equivalents seems, at least for the present, 

 justifiable. 



In the more southern portions of Canada and in the United States 

 the coral zone of the Lyckliolm-Borkholm is recognized at many 

 localities. It is well developed in the so-called Noix ooUte of Mis- 

 souri and lUinois, which holds not only the same genera, but in many 

 cases identical species of corals with distinct Silurian affinities. This 

 oolite, as well as the underlying formations of Richmond age, contain 

 the bryozoans which have been noted also in the upper Lyckholm 

 and in the Borkholm formations. Though similar to the preceding 



