INTRODUCTION 



The geology of the eastern Adirondacks presents many prob- 

 lems of interest. The townships along Lake Champlain contain 

 within their borders the contacts of the labradorite rocks — (gabbros, 

 norites and anorthosites) with the quartzose gneisses and crystalline 

 limestones ; and the later-formed unconformabilities of all these with 

 the Potsdam sandstone of the Upper Cambrian. The crystalline 

 rocks of the Archaean invite study of both igneous and metamor- 

 phosed forms, while along the old shore line are the Cambro-Silu- 

 rian sediments, unchanged, not much disturbed and often rich in 

 fossils. Remarkably little, detailed, field work upon the crystalline 

 rocks lias been done in the region since the early survey of Emmons 

 and Hall, 1835-1840. What has been written is incomplete and the 

 stratigraphical conclusions are drawn from too little recorded data. 

 A general review of these papers has been given by the writer, in 

 the Transactions of the New York Academy of Science, v. 12, p. 

 19, Nov. 1892. Emmons in his Final Report, 1842, devoted almost 

 no attention to the relative stratigraphy of the crystalline rocks 

 and not until 1870, is the question alluded to and then by James Hall 

 only as regards the age of the serpentinous limestones (Amer. Jour. 

 Sci. Oct. 1876) which are spoken of as being later than the Lauren- 

 tian and earlier than the Potsdam. Dr A. R. Leeds' paper entitled 

 " Notes on the Lithology of the Adirondacks " (Chemical News, 

 Mar. 1877, 36th Annual Report, N. Y. State Cabinet 1877, p. 79) 

 relates to the chemistry and petrography of the anorthosites and 

 trap dikes only. 



In 1879 C. E. Hall published a short condensation of what was 

 apparently expected to be a longer contribution. It is entitled Lau- 

 rentian Magnetite Iron Ore Deposits in Northern New York." 

 (32nd Annual Report of the N. Y. State Cabinet— 1879, p. 133-140.) 

 A brief outline is given of the township geology in the Eastern 

 Adirondacks, and a colored map on a small scale (3 miles to the 

 inch) accompanies the report. Mr Hall divides the Archean into the 

 1, Lower Laurentian Magnetic Ore Series. 2, Laurentian Sulphur 

 Ore Series. 3, Crystalline Limestones. 4, Labrador Series or 

 Upper Laurentian with Titaniferous Ores. The relations of 2 and 

 3 are said to be uncertain, but later, in a note, the limestone of 3 is 



