204 REPORT OP THE AMERICAN COMMITTEE. 
included in it in Vermont and Massachusetts strata Avhich have 
been shown to be Lower Silurian, and in North Carolina those 
which are below the typical Taconic ; but he was certainly the 
first to reco(i:;nize what have since been called tlie Georsjia, or 
Olenellus slates, claiming that these were beneath the Potsdam 
sandstone, while all the world was against him. If it were pos- 
sible to attach his name to that group, my sense of justice would 
be gratified. My method of accomplishing this would, however, 
be a little difi'erent from yours, as I would make the Taconic the 
u[)per member of the Cambrian, th.e St. John's group and per- 
haps the lower portions of the great Cambrian series at the west 
other and older subdivisions. 
The classification of our Paleozoic rocks by faunas alone seems 
to me one-sided, and I think the physical history of the strata 
should also be considered. We all know or believe that the 
streams of time and life have flowed on continuously in the 
world's history, and if we could obtain access to the sediments 
which have accumulated in the sea basins that have always been 
such, we should find the record without breaks; the successive 
faunas interlocking in such a way that no sharp lines could be 
drawn between them. It is only along the shores of continents, 
where subsidences have occurred and the sea has temporarily 
overflowed the land, and left groups of sediments as records of 
such invasion, that we find the history broken into chapters. 
But such subsidences and deposits were not synchronous in differ- 
ent parts of the world, therefore the succession of strata on each 
continent must be studied by itself. Even here the phenomena 
are local, not general ; the successive subsidences which resulted 
each in. its circle of sediments were not conterminous, nor equal 
measures of time. The physical evidences of these changes are 
much more strongly marked in some places than others, and 
locally the faunae intermingle in such a way as to confuse the 
lines of demarcation. Hence, the divisions of the geological 
column nuist largely be matters of convention, but in this con- 
vention stratigraphy should be heard as well as paleontology. 
In my judgment it will be found most convenient to make chief 
divisions along lines marked by great physical breaks, and so I 
would make the Potsdam sandstone, which marks a great physi- 
cal change over all the North American continent east of the 
AVasatch — inauguratinff a new era — the basal member of the Or- 
