Ailing — Problems of Adirondack Precambrian. 47 



Aet. VI. — Some Problems of the Adirondack Precam- 

 brian; by Haeold L. Alling.* 



Contents. 

 Introduction. 



1. The Grenville Series. 



Structure. 



Grenville stratigraphy. 



Stratigraphic details. 



The thickness of the Grenville. 



2. The Saranac Series. 



3. The Igneous Kocks. 



The early Metagabbro. 

 The Laurentian Granite. 

 The later Metagabbro. 

 The Algoman Series. 



The Anorthosite. 



The Gabbro. 



The term "Algoman". 

 The Gabbroic dikes. 

 Diabase and Trachyte. 



4. The Age of the faulting in the Adirondacks. 



Summary. 



Introduction. 



For our extensive knowledge of the geology of the 

 Adirondack Mountains we owe a debt to Kemp, Cushing, 

 Smyth and Newland, as well as to the later workers in the 

 field; but to these pioneers the credit is due for having 

 laid the foundations upon which W. J. Miller, Ogilvie, 

 Martin and others could build. While it is believed that 

 the major problems are, to some extent at least, solved, 

 there are many problems that have hardly been exam- 

 ined. It is because the writer's experience during the 

 last five years in the area has convinced him that certain 

 phases of the Precambrian have not received a great deal 

 of attention, and because a number of conclusions were 

 reached during a detailed investigation of the graphite 

 deposits 1 that were out of place in a bulletin of an eco- 

 nomic character, that this paper is presented. 



1. The Grenville Series. 

 Structure. 



The oldest formation in the region, as far as is 

 known, is the Grenville series of ancient sediments, 



* Published with the permission of the Director of the New York State 

 Museum. 



The writer is indebted to Professors George H. Chadwick and James F. 

 Kemp for reading the manuscript. 



1 The Adirondack Graphite Deposits, N. Y. State Mus., Bull. 199, 1918. 



