378 REPORT ON NATIONAL MUSEUM, 1886. 



oeous matter and scattering particles of amorphous pyrite, which are 

 occasionally visible, render its adaptability to outdoor work decidedly 

 doubtful. The stone is known commercially as "Madrepore marble." 

 A. polished slab 2 by 4 feet is in the collections of the National Museum. 



The light yellowish, buff, or brown sub-Carboniferous magnesian lime- 

 stone, quarried near Le Grand in Marshall County, also contains mass- 

 ive layers beautifully veined with iron oxide, and which are suitable 

 for ornamental purposes, though it is not considered suitable for monu- 

 ments and other work subject to continuous exposure. I have not seen 

 samples of this material, though it is well spoken of by White.* It 

 is popularly known as "Iowa marble." The only other stone which, so 

 Far as I am aware, has ever been utilized for ornamental purposes 

 is the so-called "Iowa City," or "Bird's-eye marble." This is nothing 

 more than fossil coral "(AcervulariaDavidsoni) imbedded in the common 

 Devonian limestone and often perfectly consolidated by carbonate of 

 lime so that it may be polished like ordinary marble. When so polished 

 its appearance is very beautiful, for the whole internal structure of the 

 coral is as well shown as it is in living specimens, and yet it is hard 

 and compact as real marble." The stone would be valuable could it be 

 obtained in blocks of large size. Unfortunately it occurs in pieces of 

 but a few pounds' weight ;t it is used therefore only for paper-weights, 

 and small ornaments of various kinds. 



Maryland. — The principal marble quarries of this State are located 

 near Cockeysville and Texas, some 1G miles north of Baltimore, on the 

 Northern Central Kail road. Here there occurs a small and isolated area 

 of Lower Silurian (?) dolomite of medium texture and pure white color 

 that has been very extensively used for general building purposes in 

 Baltimore and Washington and the neighboring towns, and to a less 

 extent in Philadelphia. In the quarries the stone lies in large horizon- 

 tal masses, and blocks 28 by 10 by 3 feet have been quarried entire. This 

 stone was used in the construction of Christ Church in Baltimore, the 

 Washington Monument, and the columns and heavy platforms of the 

 Capitol extensions at Washington, D. C. 



Near Union Bridge, in Frederick County, there occurs a fine-grained 

 and compact white magnesian limestone, but which has not been quar- 

 ried to any extent. 



The only true, conglomerate or breccia marble that has ever been util- 

 ized to any extent in the United States is found near Point of Bocks, 

 Frederick County, in this State. The rock, which belongs geologically 

 to the Triassic formations, is composed of rounded and angular fragments 

 of all sizes, up to several inches in diameter, of quartz and magnesian 

 limestone imbedded in a fine gray calcareous groundmass. This com- 

 position renders the proper dressing of the stone a matter of some diffi- 

 culty, since the hard quartz pebble break away from the softer parts in 

 which they lie, leaving numerous cavities to be filled with colored wax 

 * Geol. of Iowa, vol. 2, p. 313. t White, op. cit., p. 316. 



