« INTRODUCTION 401 



sites/' comparatively little data regarding the structure and origin of the 

 Adirondack anorthosite had been published, and all such material was 

 gathered without Bowen's hypothesis in mind. Thus many of the impor- 

 tant facts bearing on the problem were either only slightly considered or 

 not thought of at all. The only detailed geologic maps representing por- 

 tions of the anorthosite area were the following New York State Museum 

 quadrangle maps : Long Lake, by professor Gushing ; the Elizabethtown- 

 Port Henry, by Professor Kemp, and the Paradox Lake, by Doctor Ogil- 

 vie. Of these only the first two are accompanied by reasonably full de- 

 scriptions of the anorthosite, and these two maps show more or less sepa- 

 rate representations of the border facies of the anorthosite. 



It is evident, then, that published data pertaining to the Adirondack 

 anorthosite, and particularly facts bearing on Bowen's hypothesis, are 

 meager. 



None of the results of my many months of field and laboratory studies 

 pertaining to the anorthosite area, more especially those portions com- 

 prised within the Lake Placid and Schroon Lake quadrangles, but also 

 somewhat in other quadrangles, have yet been published. My last sum- 

 mer's work was done with Bowen's paper in hand. Among the many 

 observations which I have made, some strongly support Cushing's con- 

 tention that the anorthosite is a separate intrusive body distinctly older 

 than the syenite-granite series. Many of my observations, however, have 

 new bearings and these throw important light on the anorthosite problem. 

 The purpose of this paper is, then, to present and to shovvr the significance 

 of all the more important evidence, both old and new, which bears on the 

 structure and origin of the Adirondack anorthosite. 



Adirondack Rocks in General * 



The Grenville series comprises the oldest rocks of the Adirondack re- 

 gion, and they are generally considered to be of Archeozoic age. They 

 consist of a great mass of strata thoroughly crystallized into various 

 gneisses and schists, calcite marble, and quartzite. A more or less well 

 developed foliation is always parallel to the stratification surfaces, which 

 are usually distinctly preserved in spite of the complete crystallization. 

 Grenville strata are well represented throughout most of the Adirondack 

 region, their distribution being very irregular or "patchy," because they 

 have been so badly cut to pieces by great bodies of intrusive rocks. Be- 

 cause of the breaking up of the Grenville into masses great and small by 



* Detailed accounts of the rocks may be found in the various New York State Museum 

 Bulletins pertaining to the region. 



