© . 
Lesley. | 260 [Dee, 21, 
( Four of neck planes............ ooiee arenes 
@ ‘Pp’ ee cheek by back jaw and posterior skull by }- Prism. 
CAT ac tic sreteirs ler elteres oehe Selene Beal enatotutigne near : 
Of course it is understood that m, n, t, r, &c., are simply coefficients by 
means of which to derive all the forms to which they refer in parameter 
values from some typical P whose parameter values must be assumed as 
normal, 
The whole object is merely to enable the sculptor to give each plane 
a name and not entirely an arbitrary one. 
On w Series of Chemical Analysis of Siluro-Cambrian Limestone Beds in 
Cumberland County, Pennsyloania. 
By J. P. LESLEY. 
(Read before the American Philosophical Society, December 21, 1877.) 
The mixture of magnesia with lime in dolomite rocks has always stimu- 
lated and baftled geological speculation, and given birth to opposite hy- 
potheses ; some of them, such as that of the issue of magnesium vapors 
from the interior of the earth, absurd enough; others, such as that re- 
cently propounded by Mr. W. L. Green, British Minister at Honolulu, who 
derives the magnesia from olivine in lava, very suggestive of truth. 
I have long felt that no sound basis for speculation had been secured so 
long as the collection of facts consists merely of analyses of sporadic speci- 
mens of limestone and dolomite rocks. I therefore directed Mr. R. H. 
Sanders, of the Pennsylvania Geological Survey, to make a careful section 
of the Siluro-Cambrian strata exposed for a quarter of a mile along the 
west bank of the Susquehanna River, opposite Harrisburg, both by the 
deep cuttings of the North Pennsylvania Railroad, and by quarries. This 
was done in connection with his field work in Cumberland County. 
Mr. Joseph Hartshorne was also directed to take duplicate samples from 
every stratum, thick or thin, in this section ; one at railway grade, and the 
other at the top of the exposure (sometimes 30/ high) ; to analyse them in 
the laboratory of the Survey at Harrisburg. This he has done, and is still 
doing, devoting his entire time and attention to the selection of the 
samples in stu, and their determination in the laboratory. In all cases of 
doubt the analyses have been duplicated and sometimes triplicated ; and a 
report of all analyses as fast as made is forwarded to headquarters. 
Of the whole conformable series of beds numbered from the topmost 
(dipping about 30° to the south) No. 1 down to No 98, Mr. Hartshorne has 
as yet only analysed from No. 1 to No. 46. But the generalization which 
