50 PROCEEDINGS OF THE AMHERST MEETING 



make this famous locality of mineral springs a State reservation was 

 very active. Both Precambrian and early Paleozoic strata are involved, 

 but the region is a difficult one because of masking of the hard-rock geol- 

 ogy by the excessive deposits of Pleistocene sands and drift. An ex- 

 tremely careful and, for the conditions, accurate map and description 

 resulted and many valuable details were recorded, both on the Precam- 

 brian and Cambro-Ordovician strata. 



In areal work Professor Gushing next undertook the mappings of the 

 three quadrangles — Brier Hill, Ogdensburg, and Eed Mills — at and 

 around the city of Ogdensburg, thus continuing the work done in the 

 region of the Thousand Islands at a locality farther down the Saint Law- 

 rence Eiver. Bulletin 191 of the State Museum resulted in 1917. The 

 greater part of the area is covered with the early Paleozoic strata, but 

 especially interesting exposures of the Grenville are described. Granite 

 and syenite give material for comparisons with the similar rocks at the 

 Thousand Islands. 



The last field-work done by Professor Gushing in the Adirondack Pre- 

 cambrian was in the Gouverneur Quadrangle, lying east of the Thousand 

 Islands area and south of that near Ogdensburg. We have as yet only a 

 preliminary sketch in the title for 1918. The quadrangle contains some 

 of the best exposures of the Grenville in the State and many of the 

 famous old localities of the tourmalines and other silicates which have 

 gone to all the mineral collections of the world. The complete bulletin 

 will be awaited with deep interest by all students of the Precambrian. 



In these later years we note that the thoughts. of Professor Cushing 

 naturally turned to generalizations on his extended experience in north- 

 ern New York. The age of the complex series of its igneous rocks led to 

 the first title under 1915. In this paper he stoutly maintains the wide 

 difference in age in the two granites of the Thousand Islands, reviewed 

 above, and their relations with the ether definitely established intrusives 

 of the mountains. 



The laboratory investigations of N. L. Bowen, of the Carnegie Geo- 

 physical Laboratory, on the anorthosites, followed by studies in the field 

 and publication, in 1917-1918, on the broad features of their laccolithic 

 or batholithic nature in the Adirondacks, raised a question in which Pro- 

 fessor Cushing was deeply interested. In 1917 he discussed the subject 

 and supported the view that our field knowledge was of so indeterminate 

 a nature as to make very difficult the decision as to whether the anortho- 

 sites and syenites formed a huge laccolith or bathylith. 



In these later years Professor Cushing turned again to the study of the 

 Mississippian strata in northeastern Ohio, the subject on which his very 



