154 IluAllKricdll (iroJiitJtxt . Septi'iiiluT, 181)1 
is only (iO inilrs from its i)oiiit of greatest deveiopnieut on the Susque- 
hana. 
"The Hamilton sandstone is therefore a mass of (coarse siliceous mate- 
rial intercalated near the midtile of Ww group and spreading fanwise as 
from a center near Marysville. dying away and at length disappearing 
as it receded from the point." (p. 57.) 
This will uive a general description of the structure and mass of 
the Hainilton sandstone. The following is from Prof. I. C. White's 
report of Huntingdon county, and shows how the stratum occurs 
there. T., p. 105. 
Hamilton upper shale 2.")0 feet 
" upper sandstone 30 " 
" middle shale 325 " 
" lower sandstone (hard) 50 " 
" lower shale 75 " 
Thus we see that the massive Hamilton sandstone of Perry Co. , 
800 feet in thickness, has in Huntingdon Co. dwindled down to 
two comparatively insignificant sheets of 50 and 75 feet thick re- 
spectively and separated by 225 feet of shale. 
The same type of structure is shown in Northumberland and ad- 
joining counties as we find from Prof. White's report (G. p. 77, 
etc.) He says in speaking of the country east of the eastern 
branch of the Susquehana : 
"The type of the Hamilton series is remarkably similar to the cor- 
responding beds in western New York both in lithology and in the a<;- 
companying fossils." 
Again he writes : " The middle type of the Hamilton comes in after 
passing south from the Northumberland synclinal and may be found on 
both sides of the Selinsgrove arch which crosses the river about five- 
miles below Sunbury. The section on the south side of that axis exhibits 
a structure for the Hamilton (juitedifferont from that shown in Columbia 
county."' 
Olive-browu shales 450 feet 
Selinsgrove upper sandstone 202 " 
Dark olive shales 125 " 
Selinsgrove lower sandstone 5 " 
Brown and dark shales SOO " 
Again Prof. White writes : "The southern type of the Hamilton bods- 
is reached after passing south of the Georgetown axis near the southern 
border of Norrhumberland there being a progressive coarsening of the 
series in that dinuHion from the locality of the last section near Selins- 
grove." 
Selinsgrov<' upper sandstone. 100 feet 
Olive-brown shales 300 " 
Selinsgrove lower sandstone; 50 '• 
