Suburban Geology of Richmond, Indiana. 283 



possessing an unctuous feel and a great degree of plasticity. By- 

 way of experiment, I had several little articles of pottery manu- 

 factured from it, and they proved to be of finer quality than our 

 ordinary ware ; and from their lighter color, it appears that this 

 clay is not so ferruginous as that usually employed at this place. 

 Most of the strata through which the national road passes are 

 composed of calcareous matters of various degrees of hardness, 

 and of bluish argillaceous masses and sandy particles, all so in- 

 termingled as to give a very broken structure to the rock. In 

 consequence of the presence of clay, it is unfit for making good 

 lime. Two or three specimens of the more friable portions yield- 

 ed nearly one third of their weights of siliceous matter, insolu- 

 ble in muriatic acid. This argillaceous member of the blue fos- 

 siliferous limestone, is known as "marlite;" its greatest depth is 

 about twenty feet. Below this the rock is quite geodiferous, ex- 

 hibiting numerous cavities lined with beautiful calcareous spar, 

 sometimes associated with groups of minute crystals of satin spar ; 

 small guhrs of light brown compacted sand, in some instances 

 feebly effervescent with acids, are also very common ; spheroidal 

 masses of sulphate of barytes often occur ; and laminae of sul- 

 phate of strontian, crossing the pockets of calcareous spar, are 

 more rarely met with. A small specimen of galena was dis- 

 closed in one of the quarries several years ago. >^&f& 



* 



In the upper strata of this formation, I have discovered a char- 

 acter of quite a novel kind. So far as I have learned, it has never 

 been described, and perhaps not yet elsewhere been seen. It 

 consists in the presence of pisolitic balls, imbedded in every por- 

 tion of the solid rock. They average perhaps one third of an 

 inch in diameter ; and the nucleus in almost every instance ap- 

 pears to be a very small fragment of a Strophomena or some other 

 thin shell. Generally no concentric layers are discoverable in 

 them ; but in other instances the succession of delicate incrusta- 

 tions is distinctly visible. These pisolitic concretions are always 

 much lighter colored than the body of the rock, from which they 

 are not separable, but are completely consolidated with it ; its 

 fracture sometimes displays a pretty marble-like surface. Fig. 2 

 presents nearly a fac-simile of a portion of this rock. These 

 pisolitic strata vary from two to ten feet in depth j and are fre- 

 quently found blended with the "marlite." The central portions 

 of some of these concretions are a shade or two darker than the 



