VARIATIONS OF CERTAIN ADIRONDACK BASIC 
INTRUSIVES" 
WILLIAM J. MILLER 
Hamilton College, Clinton, N.Y. 
INTRODUCTION 
The basic intrusives—gabbros and diabases—discussed in this 
paper are wholly confined to the North Creek (Warren Co.) New 
York quadrangle, a detailed geologic map of which will soon 
appear as a publication of the New York State Museum. The 
region, though well within the Adirondack area, has afforded an 
unusual opportunity for detailed field work because of the numerous 
roads and trails and the large number of excellent exposures as 
compared with the Adirondacks in general. The gabbros occur 
almost always as small stocks or bosses, while the diabase always 
occurs as true dikes. In all, 61 gabbro masses and 11 diabase 
dikes have been mapped within the quadrangle. Among the 
gabbros there are many remarkable variations of primary and 
secondary origin. It is the chief purpose of this paper to describe 
and attempt to explain the primary variations, though certain sec- 
ondary features will also be briefly discussed. The writer is greatly 
indebted to Professors J. F. Kemp, H. P. Cushing, and C. H. Smyth 
for their able papers dealing with Adirondack basic intrusives, but, 
so far as the writer is aware, little or no attention has been given to 
an explanation of the primary variations of the gabbro. 
- ROCKS OF THE REGION 
The rocks of the North Creek quadrangle are all of pre-Cambrian 
age, and these given in their relative order of ages comprise the 
Grenville sedimentary series of various gneisses, quartzite, and 
. crystalline limestone; syenite and granite; gabbro; pegmatite; 
and diabase. 
The Grenville strata are all highly metamorphosed, with lime- 
stone unusually prominent in this portion of the Adirondacks. 
‘Published by permission of Dr. J. M. Clarke, State Geologist of New York. 
160 
