330 The American Geologist. May, isyy 
Report on the Boundary between the Potsdam and Fre-Catnbrian 
Rocks, north of the Adirondacks. H. P. Gushing. (Geol. Survey 
of New York, Annual Report for 1896, published in separata, 1898.) 
This is essentilly a report of field observations, accompanied by a 
map showing the approximate boundary of the southern limit of the 
Potsdam sandstone through Franklin county and to and beyond Pots- 
dam in St. Lawrence county. Under the term Potsdam are included 
all the strata of sandstone below the Calciferous, which is in accord 
with the usual practice in New York. It is probable however that 
two non-conformable (or slightly discordant) sandstones are here in- 
cluded, and that these represent the two sandstones which in the lake 
Superior region are separated by an important igneous disturbance, 
and sometimes by non-conformity, viz: the upper portion of the 
Keweenawan eruptives. 
The author improved his oppportunities to gather important data 
concerning the pre-Cambrian rocks, and his occasional comments on 
their nature and structures are very suggestive. For instance, in his 
account of the "sequence of geologic events in the Adirondacks" (p. 
9) he states that, though there are three series of gneisses, normally, 
yet the first two so completely grade into each other that it is ques- 
tionable whether there should be any attempt to separate them; while 
the third grades into augite-syenytes and gabbroitic rocks, passing into 
them either by insensible gradations or becoming finely interbanded 
with them. "They also seem to grade into the basic gabbros of the 
region; at least these present phases practically not to be distin- 
guished from them." The gneisses of this series, which appear to be 
younger than the others, and perhaps the equivalent of the Grenville 
of Logan, diflfer widely from the others, and appear in large part 
to be "unquestionably of sedimentary origin," with complete loss of 
clastic structure. These statements, when coupled, point to the pos- 
sible or the probable sedimentary origin of some phases of the basic 
gabbros into which the sedimentary gneisses seem to grade. This is 
an important result of field studies, and is entirely in keeping with 
observations made by the writer on the relations of certain schists 
and basic gneisses to the muscovadyte rock which is one of the phases 
of the great gabbro mass of Minnesota. n. h. w. 
Augite-syenite gneiss near Loon lake. New York. H. P. Gush- 
ing. (Bull. Geol. Soc. Am., Vol. X, pp. 177-192, Apr. 1899.) 
In this more detailed study the author gives further important data 
concerning the petrographical and chemical as well as the structural 
relations of some syenytes to certain quartzose sedimentary gneisses 
which lie alongside, having the same direction of foliation, dip and 
strike. The general impression is that the two constitute a regularly 
bedded series, but from general considerations based on preconceived 
ideas and on the chemical composition he concludes that the augite 
syenyte is an igneous rock. 
The microscopical description recalls the augite-syenytes of the 
Keweenawan rocks of the Lake Superior region, which in a 
