82 CONTRIBUTIONS TO THE GEOLOGY OF MAINE. [bull.1$5. 
Arisaig fauna, D of Honey man's section, which was ''unhesitatingly 
referred to the Ludlow Tilestone" by Salter in 1862. l 
This Chapman sandstone fauna is the latest marine Paleozoic fauna 
so far recognized in Maine, unless the Moose River fauna with Oris- 
kany species be a little later. It is contained in a massive brown sand- 
stone and argillaceous layers stratified therewith. Its comparison with 
other faunas links it with the so-called Oriskany of the Moose River 
region farther west, and also with the early beds of the Gaspe sand- 
stone farther east. For this general region it is a representative of 
the transition zone from calcareous formations, which are unmistak- 
ably Lower Helderberg in age, up to coarse gray and red sandstones 
containing Devonian plants, reported to be 7,000 feet thick on the 
Gaspe Peninsula and to represent the Old Red sandstone phase of the 
Devonian system. 
The fauna contains some twenty-five or thirty good species, a few 
of which can be identified with species of the Tilestone and Upper 
Arisaig faunas already described. A few Gasp6 species described by 
Billings are closely approached; but, as a fauna, the resemblance to 
the typical Tilestone species of Murchison's Silurian system is most 
striking and suggestive. 
The faunas, 1099 A, B, and C, are given on previous pages (see 
pp. 79, 80). 
The significance of the correlation of this Chapman sandstone with 
the Tilestone of Murchison is found in the fact that the Tilestone con- 
tains the topmost fauna of the original Silurian system of Murchison. 
This fauna was described b}^ Sower by in The Silurian System (1839), 
and afterwards the Tilestone was placed by Murchison himself in the 
Silurian (Siluria, 1854). This change was brought about by the 
recognition by Murchison that paleontologic evidence is of greater 
importance in the determination of the age of rocks than petrographic 
evidence. By the study of The Silurian System it is perfectly evi- 
dent that the Silurian system was intended by Murchison to include all 
the fossiliferous formations lying below the Old Red sandstone. We 
find this indicated clearly on pages 3 and <±, and still more clearly 
expressed on page 7, of the introduction of The Silurian System, 
where are found the following words (referring to the name Silurian) : 
"The term was no sooner proposed than sanctioned by geologists, both 
at home and abroad, as involving no theory, and as simply expressing 
the fact that in the ' Silurian region ' a complete succession of fossilif- 
erous strata is interpolated between the Old Red sandstone and the 
oldest slaty rocks." We find that the reason for including the Tile- 
stones in the Old Red was the fact that the soil weathered out reddish 
in the same way as the Old Red sandstone did where it was typically 
represented. These tilestones, however, were not always red in them- 
i Quart. Jour. Geol. Soc, Vol. XX, 1864, p. 334. 
