Fea Ree PO IER ea Te cig ga wed Pec, tinecne NOG f Sake Oy aoe ene ae a Praeger ge ae 
is i ? : Z eae 
H. M. Chance—The Millstone Grit. 185 
Geol. Survey of Pa,, 1879). The same conclusion was simul- 
taneously reached by Mr. Carll in the oil regions (Reports I 
and ill) and afterwards by Professor White in his reports on 
the Ohio line counties (Q, QQ, QQQ); and it now appears that 
Professor Green and his colleagues were at the same time 
working out a strikingly similar structure in this rock in the 
Yorkshire district. The nomenclature first adopted by these 
geologists is compared in the following table with that adopted 
by Professor White and myself: 
YORKSHIRE. PENNSYLVANIA. 
“ Rough Rock.” Homewood Sandstone. 
Shales (sporadic coals). Mercer coal group. 
“Second Grit.” Connoquenessing Upper Sandstone. 
Shales (coal). Quakertown coal. 
“Thi it.” Connoquenessing Lower Sandstone. 
Shales (coal). Sharon coal. 
“Kinder Scout Grit.” Sharon (or ‘‘ Ohio’) Conglomerate. 
Over large areas this nomenclature is easily and naturally 
applicable to all vertical sections in both Yorkshire and West- 
was therefore found necessary to generalize the Yorkshire 
scheme by including these in one subdivision under the name 
“ Middle Grits,” thus: (Geol. of Yorkshire, p- 82). 
“Roueu Rook or Topmost Grrr. 
SHALES. 
MippLE Grits.—A group of sandstones and shales, variable in number, 
thickness and character. ; 
Millstone Grit 
HALES, 
Kinper Scout or Lowest Grits.” 
In Western Pennsylvania a precisely similar generalization 
has been resorted to (Report V, pp. 188 and 223), thus: 
— ( Homewoop SAnpsTONE. 
1 MERCER GROUP,—coals, etc. 
CONNOQUENESSING GROUP,—sandstones. 
[ SHARON GROUP. 
“OHIO” OR SHARON CONGLOMERATE. 
i 
Conglomer- 
e, No. XI 
os 
The Homewood Sandstone is a hard, massive conglomeritic 
rock ; the Rough Rock is also of this type and is used as 
key-rock just as the former has been used in Pennsylvania. 
The Kinder Scout Grit is hard, massive, coarse and often con- 
glomeritic, and is also used as a key-rock ; while in Pennsyl- 
vania the Sharon Conglomerate (or Olean, Garland or Mead- 
ville rock) has likewise been a most valuable guide. It is 
usually hard and massive and often a true conglomerate. 
When capping the hilltops it forms prominent ‘rock cities.” 
Am. Jour. Sco1.—Turrp igen Vou. XXI, No. 122.—Frs., 1881. 
