ite Pw OGiNPriCAL PROVINCE .Oh ESSEX 
COUNTY VENSS == I. 
THE area of igneous rocks in Eastern Massachusetts, especially 
in Essex county, has been, as the late Geo. H. Williams said, 
‘‘more discussed than any other similar region of the continent.” 
But, while it is the subject of a considerable literature, no petro- 
logical study of the region hasbeenmade. A few investigators, 
notably Wadsworth and J. H. Sears, have described the rocks, 
but there has been little or no attempt to codrdinate the results 
and to compare this region with other analogous petrographical 
provinces, although its resemblance to that of Norway has been 
noted by Rosenbusch, Brogger and others. It is with the aim 
of supplying this deficiency that these pages are written. 
I have visited the region of Essex county several times and 
collected a large number of specimens from the various locali- 
ties, so that my collections are fairly representative of the differ- 
ent types, and my knowledge of their occurrences and relation- 
ships sufficient to justify me in undertaking the present investi- 
gation. This paper will deal with the subject in a purely 
petrological way, since the general geological, structural and 
stratigraphical features are far too complex to be unraveled in 
occasional visits such as mine were. A number of occurrences 
of dike and other rocks which merit a more detailed description 
than is here possible will be published separately, probably, in 
the American Journal of Science. 
I would express my sense of deep obligation to Mr. J. H. 
Sears, of Salem, who has made this region an object of study 
for many years and whose acquaintance with it is unequaled. 
He has been most cordial and liberal in giving me specimens 
which it would have been difficult for me to obtain otherwise, 
and has encouraged me most generously in undertaking the 
present investigation. 
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