Rules and Misrules in Classification. — Marcou. 43 
Thk Phillipsburgh and PoiNTE Levis formation. 
We come now to the second misrule in the classification of 
strata belonging to the lower Paheozoic rocks. Dr. Emmons 
recognized below the Calciferous group the Potsdam sand- 
stone, which according to his observations is the bottom group 
of the Champlain division : and below the Potsdam he saw 
an enormous series of strata, 25,000 feet thick, mainly slates, 
which he called most appropriately the Taconic system. At 
different levels in that system Emmons found magnesian lime- 
stone, son)e of which he called Stockbridge limestone, or 
marble, of Berkshire county. 
He was confronted with a stratigraphic anomaly, which as- 
tonished him considerably, finding now and then a limited 
deposit of limestone, generally more or less magnesian, but 
sometimes of pure or even marly limestone. These deposits, 
he thought, were pockets of more recent limestone deposited 
in holes of the slates (Taconic slates) and belonging, accord- 
ing to a few fossils collected at different localities, to the Cal- 
ciferous group, or to the Chazy and Black River divisions, or 
even to the Trenton limestone. Dr. Emmons maintained that 
there was a well marked discordance of stratification between 
those beds of pocket limestones and the Taconic slates sur- 
rounding them. It is true that a sort of unconformity, or, 
more exactly, of diffuse stratification exists between the slates 
and the small islets of limestone, due to the structural nature 
of these islets, which I admit are rather puzzling and difficult 
to account for. The first time I came in full view of some of 
them round St. Albans, Vermont, in 1861, I had no difiSculty 
to see that they were lenticular masses of magnesian lime- 
stone, deposited at the same moment and inclosed in the 
slates, and consequently contemporar}^ with the slates. But 
at Phillipsburgh. Canada, those islets of limestone are so nu- 
merous and so elongated as to present — at first sight — the as- 
pect of a regular deposit of limestone analogous to the depos- 
its of the Chazy limestone at Chazy village. It was when 
working out the stratigraphy of Poiute Levis, opposite Que- 
bec, in 1861 and 1862, that at last I became convinced that 
all those outcrops of limestone were inclosed in the slates and 
of the same age as those slates, and that the fossils found, 
now and then, in some of those limestone islets, instead of in- 
