316 New Yoek at the World's Columbian Exposition. 



edge of the geological formations of New York State whicli have so 

 far heen placed on record. 



Although New York is tlie mother State in geological nomenclature 

 and contains a more complete and extensive series of the formations 

 below the carboniferous than any other State, and though the rocks 

 have been studied for more than sixty years by professional geolo^sts 

 and students, our recorded knowledge of geological detail is far irom 

 complete. This is especially true of the Pre-cambrian formations which 

 consist of metamorphic and igneous rocks. This is not, however, 

 very remarkable when we consider that accurate methods of rock study 

 and classification have had their greatest development since 1873 when 

 the microscope was successfully applied to the study of rocks. In 

 mapping the Pre-cambrian formations of New York the author is, there- 

 fore, un'able to give any great amount of detail. In "Westchester, Put- 

 nam and southern Dutchess counties his personal studies during a num- 

 ber of years, with tlie assistance of Messrs. E. M. Blake. and H. Eies, 

 have enabled him to difEerentiate the areas of metamorphosed palaeozoic 

 limestones and schists from the subjacent gneisses which can be traced 

 northward through Westchester county and are apparently continuous 

 with the stratified beds which rest upon the granitoid g-neiss and granite 

 of Putnam county. The small scale of the map makes it impossible to 

 show the full detail of these narrow belts of rock which owe their 

 existence to the folding and erosion which has taken place within that 

 region. Within the Pre-cambrian area of Putnam county, which is 

 generally known as the " Highlands," in addition to the stratified 

 gneisses which contain the beds of magnetite, there are Wge masses 

 of granite which appear along the axes of the mountain folds, being 

 flanked by the stratified gneisses. The author regards these as meta- 

 morphic granites made plastic in the process of mountain making which 

 created the folds in which they occur. No attempt has been made to 

 differentiate these granites in the mapping, nor has any field work been 

 undertaken with this end in view. The southwestern extension of 

 this Pre-cambrian area through Rockland and Orange counties into 

 New Jersey has precisely the same component rocks and structure. 

 Besides the " Highland " Pre-cambrian area just mentioned, there is the 

 greater area of the Adirondack wilderness. This is known to include 

 two principal formations of Pre-cambrian age. First, an area of meta- 

 morphic stratified rocks, extending from Lake Champlain to the Black 

 river and from southern Fulton county nearly to the Canadian boundary. 

 Secondly, in the eastern part of the wilderness and touching at two 

 points the shore of Lake Champlain is a mass of basic plutonic rock 

 chiefly composed of hypersthene and labradorite which may be called 

 norite. In the work of the original Natural History Survey of New 

 York, which culminated in the publication of the reports on the four geo- 

 logical districts of the State in 1 842 and 1843, this region was investigated 

 by Prof. Ebenezer Emmons. This geologist recognized clearly the strik- 

 ing lithological differences between the massive norite and the stratified 

 gneisses which environed it, but gave no accurate description of their 

 boundaries, doubtless for want of an accurate map of the wilderness. 

 In 1883 a map of Essex county by C. E. Hall was published in the 



