'''' Level of no Strain^ — Claypole. 83 
the "Llandeilo flags," the two will be termed "Loioer Silurian rocks." 
A wood cut is annexed, explanatory of the manner in which these 
deposits are connected with the old red sandstone above them, with 
each other, and with the slaty grauwacke rocks beneath them. 
Although the lower Silurian rocks are frequently unconformable to 
the schistose grauwacke, as represented in the wood-cut, there are 
situations in which a passage from one to the other may be detected. 
Having alluded to a work which is in preparation upon the geology 
of the country of the Silures, and of several of the surrounding count- 
ies, I may take this opportunity of acquainting those friends who 
have fostered the undertaking, that the author is unceasingly occupied 
in promoting its completion. Geologists are not, I am sure, among 
those who feel surprise at the delay ; for they well know that so large 
an area of country, and one so little previously examined; could not 
have been adequately described without several years of hard labor. 
In the mean time I may state that a man is now constructing, being a 
precise reduction of the Ordnance Maps, extending over the greater 
part of ten counties, all of which have been geologically colored in the 
field ; together with about twenty plates of engravings of fossils, many 
of which are of new species, and a vast number of colored sections, 
vignettes, &c., all of which will, I trust, be completed so as to enable 
me to lay the work before the public in a few months. 
P. S. Authorities diflfer in opinion concerning the exact geographical 
boundaries of the kingdom of the Silures, &c., &c., &c. 
ILLUSTRATION OF THE "LEVEL OF NO STRAIN" IN THE 
CRUST OF THE EARTH. 
E. W. Claypole, Akron, O. 
Investigations regarding the condition of the interior of the 
Earth have been recently stimulated and directed in no slight 
degree by the publication of various papers by Messrs. Read, 
Davison, Darwin and Fisher. These workers on the physico- 
mathematical side of the subject have introduced to the notice 
of geologists a condition previouslys overlooked, but never- 
theless of very great importance. As a deduction from the 
physical laws that govern the constitution and condition of the 
deeper parts of the globe, lying beyond the reach of direct 
observation, this inference commands attention. Whether it 
finally proves to be exactly as its investigators claim or not, 
the investigation itself will be of very great advantage to the 
science by clearing and sharpening our conceptions upon a 
very difficult topic. 
A short summary of the progress that has been made in 
