410 



REPORT OF STATE GEOLOGIST. 



hhe study of a limestone fauna as well as the comparatively limited 

 amount of study outside the Pelmatozoa which it has received, 

 make the fauna of the Laurel limestone, as here listed, less com- 

 plete and representative of the formation than that of the Wal- 

 dron shale. Too little is known of the Anthozoa of the Laurel lime- 

 stone to make profitable the comparison of the representatives of 

 that group in the two faunas. The entire absence from this list of 

 the Bryozoa and their abundance in the Waldron fauna is with- 

 out significance except as indicating that the conditions of preserva- 

 tion are incomparably better in the Waldron shale than in the 

 Laurel limestone, and that no attempt has been made to study the 

 material which is preserved in the limestone. 



In the case of the Pelmatozoa, however, the faunas are probably 

 equally well known and consequently invite comparison. The crin- 

 oids described from St. Paul were obtained largely by local col- 

 lectors, who secured very complete collections of these fossils, so 

 that it is safe to assume that this part of the Laurel limestone 

 fauna is known with a fair degree of completeness. Comparison 

 of the representatives of the groups in the two faunas shows 26 

 species in the Waldron and 28 in the Laurel limestone fauna. Not 

 a single one of these, however, is common to the two faunas. A 

 complete change in the crinoidal life of the time seems to have 

 been introduced in this province with the initiation of Waldron 

 shale sedimentation. This element of the Waldron fauna evidently 

 came into this region from some outside area at the close of the 

 Laurel limestone interval. It does not appear to have been pres- 

 ent in the region at any earlier period in the Silurian and cannot 

 be considered in any degree a recurrent element of the fauna. If 

 it had been present at all during any earlier period in this region 

 the Pelmatozoa of the Waldron fauna might be expected to appear 

 in the Osgood beds, which represent sedimentary conditions very 

 similar to those which produced the Waldron shale. Comparison 

 of the listed Pelmatozoa of this fauna, which numbers 56 species, 

 shows, however, that none of the Waldron species are present in it. 



Comparison of the Brachiopoda of the Waldron and Laurel 

 limestone faunas shows a marked contrast with the results noted 

 for the Pelmatozoa. A comparatively small number of brachiopods 

 is known from the Laurel limestone, altogether, but of these all 

 but three occur in the Waldron fauna. One of the three is Platy- 

 strophia dentata; the other two have not been determined specif- 

 ically. Of the Brachiopoda in the two faunas the comparison 



'Am. .Tour. Sci.. Vol. XVIII, 1904, p. 341. 



