REVIEWS 85 



The part devoted to systematic paleontology contains the descrip- 

 tion of some two hundred species and varieties, of which sixteen are 

 new. Most of these are figured on the fifty-eight plates. There is also 

 a bibliography of Cambro-Ordovician literature. 



A. C. McF. 



Contributions to the Fre-Cambrian Geology of Northern Michigan and 

 Wisconsin. By R. C. Allen and L. P. Barrett. The Geology 

 of Limestone Mountain and Sherman Hill in Houghton County, 

 Michigan. By E. C. Case and W. I. Robinson. Michigan 

 Geological and Biological Survey, Publication 18, Geological 

 Series 15, 1915. Pp. 189, pis. 12, figs. 15. 

 Part I consists of a number of contributions on the geology of an 

 area lying west of the Crystal Falls and Iron River districts, and extend- 

 ing south of the Marquette and Gogebic iron ranges to the state line and 

 into Wisconsin beyond. The region is a great Huronian interior in 

 which the better-known and structually distinct ranges on its north and 

 east borders coalesce and lose their identity. The authors are unable 

 to say that rocks older than the Huronian are present, but find that the 

 area heretofore mapped as Archaean and undifferentiated pre-Cambrian 

 is in reality Huronian. The outstanding feature of the region is the 

 presence of an enormous granite mass intruded into the Lower and 

 Middle Huronian sediments, constituting a great batholith which seems 

 to occupy many thousands of square miles in northern Wisconsin, and 

 is represented by outlying remnants in the east end of the Gogebic range 

 and southwest and east in Michigan. The contributions consist of the 

 descriptions of the geology of a number of districts and ranges, together 

 with discussions and some revisions of the correlations of the pre- 

 Cambrian rocks of the region. 



An important conclusion arrived at by the authors is that the forma- 

 tions heretofore included in the Upper Huronian are separable into two 

 groups by an unconformity of the first magnitude. For the upper one 

 of the two the name Copps is proposed. 



Part H: Limestone Mountain and Sherman Hill are outliers of 

 Paleozoic dolomite found in Houghton County. The stratigraphic 

 range is from the Cambrian to the Middle Devonian, including the 

 Cambrian Upper Black River, Decorah, Upper Galena, Richmond, 

 Niagaran, and Middle Devonian. Behef in the presence of the Devonian 

 is based on a piece of float found on the hillside. The structure has 



