NIAGARA LIMESTONE, 371 



ively, in the formation of these ancient reefs as they do in modern 

 ones. In the northern counties, the Racine strata present no indica- 

 tions of this reef formation, but in Ozaukee and Washington counties 

 it becomes pronounced and extends thence southward until, south of 

 Racine, the formation is concealed completely beneath the drift. The 

 line of reefs is unquestionably sixty miles in length, and may be 

 much more. From their position they must be regarded as of the 

 nature of barrier reefs. It is worthy of remark here that the reefs 

 terminate at the north at that point at which the underlying forma- 

 tions undergo the modifications previously described, and it is partic- 

 ularly worthy of notice that this is the point where the Waukesha beds 

 give place to the Byron and Coral beds, from which it appears that 

 the discrimination of these subdivisions has an historical and dynam- 

 ical importance. The consideration of the industrial value of this 

 formation will be found following the treatment of the Guelph beds. 

 Dr. F. H. Day, of Wauwatosa, through years of industrious accu- 

 mulation, has gathered, from the several localities of this formation 

 in the southeastern part of the state, a very extensive collection, that 

 is exceedingly rich in new, interesting, and typical forms. He has 

 very kindly furnished the survey a list of species found at the several 

 localities, which is incorporated in the following table. The species 

 given on the authority of Dr. Day are marked thus f, those of the 

 survey, thus, *. 



