256 TJic A^ncrican Geologist. October, 1899 
spond to the ditroyte and foyayte of Brogger, the latter predominat- 
ing. An analysis is given for each type, the only notable difference 
being that the foyayte is rather richer in soda and poorer in iron 
oxide than the ditroyte, while both are notably poorer in lime and 
magnesia than the nepheline syenytes of other regions, and higher 
in silica than the average, agreeing closely with the albite-rich litch- 
fieldyte of Bayley. Next comes, as a facies of the nepheline syenyte, 
and showing the same structural distinction, the nepheline-poor to 
nepheline-free rock known as pulaskitic syenyte or pulaskyte. An 
analysis of each phase of this rock shows that it is decidedly more 
acid than the normal type of nepheline syenyte. This series closes 
with the orbicular syenyte, which occurs as rounded inclusions in 
granite and owes its name to the fact that each prominent phenocryst 
of hornblende is surrounded by a narrow zone of white feldspar. Es- 
sexyte, described as essentially a basic monzonitic rock containing 
both lime-soda and alkali feldspars and feldspathoids, is confined to the 
immediate vicinity of Salem Neck. It is ciuite distinct from the nephe- 
line syenytes, by which it is cut, but grades into the diorytes. Sears 
regards it as the earliest crystallized and most basic portion of the 
nepheline-syenyte magma. Several structural and mineralogical va- 
rieties are recognized, and an analysis of a specimen selected by Sears 
as representing the type shows a decidedly basic rock (SiO>, 46.99) 
rich in lime and soda. Dioryte has a large development in Essex 
county. It is highly varied and represents transitions from the es- 
sexytes to the akerytes. The analysis shows a rather basic rock for a 
dioryte (SiO^, 51.82), but, on the other hand, both the silica and alka- 
lies are too high for a gabbro. Besides the main type of dioryte, 
which is often more or less quartzose, the author describes a quartz- 
augite-dioryte and a porphyritic dioryte, with an analysis of the latter. 
The gabbro of Nahant is next described, and the analysis shows that 
it is low in silica (43.73) and rich in lime (10.99) as a gabbro should 
be, but also rather poor in magnesia, high in titanium oxide and 
alumina, and rather high in alkalies, for a gabbro. The hyperitic es- 
sexyte of Rosenb.usch, called also hyperitic dioryte in one of the earlier 
papers of this series, is shown by a later analysis to be more properly 
a hornblende-gabbro (Si02, 45.32). The dike rocks next receive atten- 
tion, beginning with the granitic dikes. These include aplyte, the 
very narrow dikes of which are wholly confined to the granite, with 
which they are found to agree closely in composition, and quartz- 
syenyte-porphyry, which is found to be essentially identical in, compo- 
sition with the nordmarkyte. The rocks of the paisanyte-solosbergyte- 
tingnayte series all form dikes, although of paisanyte but a single dike 
has been observed, the analysis of which is almost identical with the 
aplyte. The solosbergyte forms numerous dikes, which are described 
in detail, with two original analyses and one quoted from Rosenbusch. 
Three tingnayte dikes are described, with two analyses, the more 
basic analysis representing an analcite tingnayte. The basic include 
(likes of camptonyte (one analysis), vogesyte, very numerous dikes 
