78 CONTRIBUTIONS TO THE GEOLOGY OF MAINE. [bull. 165. 
These species are taken as they are defined, without attempt to pass 
judgment as to the propriety of drawing the specific lines as they are 
represented. The attempt to closely correlate the specimens with some 
particular species diverts the attention from the evolutional laws which 
the evidence contains and illustrates. 
In the above discussion attention is directed to the variations and the 
differences which are expressed in the dominant characters, or what 
might be called the habit or fashion characteristic of the whole group 
of rhynchonellas living at each successive stage. And it is the study 
of these peculiarities in the prevailing characteristics of a group of 
forms whose likeness suggests genetic affinity that promises to give 
us the means of detecting, in the fossils themselves, their position in 
the evolution of the race. 
For this purpose, of course, it is necessary to have before us a suffi- 
ciently full representation of the group of species to show what are 
the dominant species of the fauna. 
This study of a single group of species has demonstrated the fact 
that the evolutional stage of the group is indicated with precision, 
independent of the names of species, and independent of the fact that 
the specimens actualty present in the Maine fauna agree precisely in 
scarcely a single case with those of any fauna of New York. 
From this study it is evident that the Square Lake fauna is taxonomi- 
cally the equivalent of the Delthyris Shaly limestone fauna of New 
York. The other species in the fauna bear out the same conclusion, 
both by the absence of species of lower and higher stages and by the 
presence of characteristic forms. The habit of the species of this 
group of rhynchonellids also suggests closer relationship to stages 
earlier than the Delthyris Shaly limestone of the New York section 
than to later stages. 
The satisfaction attained by this method of correlation is the excuse 
for presenting it in this imperfect manner at the present time. Its 
elaboration and full presentation is reserved for future publication. 
CHAPMAN SANDSTONE. 
Presque Me Brook. — The typical exposure of the Chapman sandstone 
is along the east (right) bank of the south branch of Presque Isle Brook, 
about a mile from the south line of Chapman Township and about a 
mile west of Tweedy's, on the road running southwest from Presque Isle. 
The fossils and the locality were first brought to the writer's notice 
by Olaf O. Nylander, of Caribou, from whom the fossils were purchased 
for the Survey. In 1897 the locality was visited by the writer. Mor^e 
fossils were collected, and the character of the formation was observed. 
The station number is 1099 A. The rocks are mainly thick-bedded 
sandstones, with some shaly layers, and are exposed for a quarter mile 
