228 The Aincrican Geologist. April, 1898 
since its principal component, the anorthosytes of the region, 
has been found to be of igneous origin, and hence not a reliable 
integral in a stratigraphic scheme. The Lower Laurentian, 
or Laurentian proper, is divisible into two parts, viz: the fun- 
damental gneiss proper, known also as the Ottawa gneiss, and 
the Grenville series. In the Grenville series are limestones, 
quartzytes and other interstratified beds which were undoubt- 
edly derived originally from sedimentary deposition, and this 
series, according to later observations, lies non-conformably 
on the Ottawa gneiss. It is not known what chronologic 
relation the Upper Laurentian, later known as the Norian, 
bears to the Grenville series, except that it is of later date. 
It may have been its immediate successor, or there may have 
been a long interval of time, not there re])resented in the 
stratigraphy, which elapsed between their dates of formation. 
General considerations, however, of stratigraphy and of litn- 
ology which the writer has presented elsewhere indicate that 
there was no important interval of time between them, but 
that probably the event which closed the Grenville age was 
the anorthosyte invasion. General considerations also show 
that it is probable that the Grenville series is represented in 
the Adirondack mountains, where a similar series of gneisses 
associated with anorthosyte is widely extended. This series, 
characterized by marbles and quartzytes, extends into Ver- 
mont and southward to New York and into New Jersey. In 
Vermont and in New Jersey it is found that the limestones 
are fossiliferous with Taconic trilobites, and that the series is 
hence of Lower Cambrian age. 
It appears probable, therefore, that the Laurentian of 
Canada, as recently re-defined by some of the Canadian geolo- 
gists, is divisible between the xA,rchean an.d the Lower Cam- 
brian, and hence that the divisions which have been given to 
the Archean in that country cannot be the ecjuivalent of 
divisions wdiich appear in Minnesota and in Finland. In 
other words, it is probable that the divisions above detailed 
for Minnesota and Finland are wholly eml)raced in the lower 
division of the Canadian Laurentian. i. e., in the Ottawa 
gneiss, and that they have not yet been noted in Canada. How 
much of the Ottawa gneiss is to be attributed to the metamor- 
jjhosed condition of fragmental strata which in other places in 
