636 GEOLOGY OF OHIO. 
that some of them produce, have led to very large use of the stone, 
especially in the government works along the line of the great lakes. 
Latterly they are losing their place as building stones to some extent, 
but the production of lime has increased. Some quarries have been 
worked for at least fifty years. In these quarries the lower 6 or 8 feet 
are cemented into one solid sheet from which the large dimension stones 
for which the location is famous are extracted. It is from these quarries 
that a large part of the heavy stone used in the Sault Ste. Marie canal, 
in the northern light-houses, and in other government works has been 
derived. Many of the most important public and private structures in 
the region of the great lakes were built of the Marblehead stone. The 
Detroit and the Cleveland water-works, the light-houses at Spectacle 
Reef, Marblehead (built over fifty years ago), and Stanard’s Rock, Lake 
Superior, were all wholly or partly built of this material. It is particu- 
larly valuable in situations where it is exposed to the action of water 
or frost, as is shown by the condition of the old locks of the Sault Ste. 
Marie Falls canal and the light-houses in exposed situations. 
The material from these quarries, like that at Sandusky, is a 
magnesian limestone, which contains beautifully preserved fossils ; the 
centers of the little rhombohedral crystals that characterize all of the 
Sandusky limestone are free from the grains of pyrites which characterize 
the blue Sandusky layers, and the difference in the color of the two stones 
isto be attributed to this circumstance. 
The following analysis, made by Mr. J. Lang Cassels, represents 
the composition of the limestone from these quarries: 
Per cent. 
Cal cium, Car bOnate: ac cinvcceceevenedecn eee mete ree eee a eee oe ease nee aaaicere ae 83.20 
Magnesian carbonate au. ssi-sscccecss splecnecsence er ctceci insite oitcceecieesiee astss 15.83 
SUT Cais csc neta seh catncoes antes cleanin Gua ee as nee Mie oe nee eR ETA Ie eral nS Nears tats 0.15 
OreaniGoMmatteisecds cedcekstascevetoarececeecee ce ee eee eee eee eee ceca ae aee 0.02 
IMIGIStUREHeecseeet see ere eee sees eee dates coe enon n teste Sateen eM ee Ce aeae teats 0.80 
8 Woy) Reena ener ane eer acre aon oc rnditicemnopdasoad oscdcccododided 100.00 
The proprietors claim that they could easily extract a block of stone 
equal in size to the Egyptian obelisk recently introduced into this 
country, its extraction being simply a matter of expense. 
The block-stone proves to be a source of excellent lime, which has 
long been used, but which of late has been more abundantly produced. 
