410 C. K. LEITH 



separation. The anorthosites have intruded and metamorphosed the 

 limestones and quartzites, and probably some of the gneisses. It has 

 been noted that the anorthosite frequently passes outward by gradual 

 transition into the dark gneisses with labradorite augen. Cutting all 

 the above rocks are trap dikes, but whether pre-Cambrian or later, is 

 unknown. 



GENERAL COMMENT ON THE ADIRONDACK WORK 



The above conclusions are of much interest as bearing on the 

 general problems of the origin and age of the gneisses associated with 

 the limestones of the Adirondack region. Kemp, 1 working on the 

 eastern side of the district, has previously concluded that it does not 

 appear certain that in the eastern Adirondack region there are any 

 rocks older than the clastic series. As a result of field work on the 

 eastern and western sides of the district, Van Hise 2 has held that most 

 of the gneisses are clastic, but that a part of the red gneisses may be 

 older than the clastic series, and therefore of Archean age. From the 

 above summaries it appears that Kemp in his recent work still main- 

 tains the absence of the Archean. Cushing, working mainly in the 

 northern part of the region, although overlapping Smyth's area a little 

 way on the west, places in a lower series gneisses which he believes to 

 be in part at least of Archean age, holds that a considerable portion 

 of the gneisses associated with the limestones are unquestionably of 

 sedimentary origin, and offers no evidence to show that any of the 

 gneisses associated with the limestones are igneous and later than the 

 limestone. Smyth, working entirely on the western side of the region, 

 concludes that the presence of the Archean or basement gneiss has 

 not been shown; that certain of the gneisses associated with the lime- 

 stones may be sedimentary; but that the greater part of the gneisses 

 of the district are igneous and later than the limestone. He thus 

 agrees with Kemp on the point of the absence of the Archean. 



It is to be remembered that Kemp, Cushing, and Smyth have 

 been working in 'different areas. Each of them may be right as to 

 the origin of the gneisses of his area and there may be present in 

 the Adirondack district Archean, Algonkian, and post-Algonkian 

 gneisses. Such is approximately the case in the Lake Superior region, 



'Bull. G. S. A., Vol. VI., 1895, p. 251. 



2 Bull. 86 U. S. Geol. Survey, 1892, pp. 413-414, and sixteenth Ann. Rep. 

 U. S. Geol. Survey, 1896, pp. 771-773- 



