Reviews 



Geology of the Northern Adirondack Region. By H. P. Gushing. 

 (New York StSiteyLuseum. Bulletin No. gj, 1905.) Pp. 271-454, 

 18 plates and 9 figures. 



About a year earlier Professor Gushing published Bulletin No. 77 of 

 this same series, in which the "Geology of the Vicinity of Little Falls, 

 Herkimer Go. [N. Y.]," was admirably described. The present bulletin 

 is devoted mainly to the geology of Glinton and Franklin Gounties, but 

 one interested in the geology of the Mohawk Valley will find in the 

 descriptions and comparisons much of genuine interest. Professor Gush- 

 ing's reputation as a petrographer guarantees an accurate and valuable 

 study of the pre-Gambrian rocks which cover so large a part of the area 

 under consideration; but the reader interested in the structural geology 

 and Paleozoic formations of northern New York will also find it a most 

 interesting report. The figures, colored geological maps, and excellent 

 plates giving views of typical outcrops of the various formations, add 

 greatly to the attractive appearance of the bulletin. 



Under pre-Gambrian history it is stated that the oldest rocks certainly 

 recognized in the Adirondack region consist of well-banded gneisses and 

 schists with bands of coarsely crystalline limestone, believed to be water- 

 deposited rocks which are referred to the Grenville formation of Ganada. 

 In parts of the region is a mass of gneisses of doubtful age and formation, 

 thought, however, to be of igneous origin, which are given the name "Sara- 

 nac formation " from the exposures along the river of that name in Glinton 

 Gounty. Professor Gushing states that "after the present surface rocks 

 had become deeply buried, they were invaded from beneath by a series 

 of great igneous intrusions, broken up into patches." These igneous rocks 

 are grouped into the following four classes : anorthosites, syenites, granites, 

 and gabbros. 



Pre-Gambrian time was very long, and the amount of erosion very great, 

 so that Professor Gushing estimates that in this region "in all likelihood 

 at least from three to five miles of rock thickness were worn away from 

 the surface and perhaps considerably more, especially locally." 



In early Paleozoic time a subsidence began in the northeastern part 

 of the area and slowly moved to the southwestward. On account of over- 

 lap, the oldest Paleozoic formations, those of Lower and Middle Gambrian 



657 



