On the Fossils of the Eastern Portion 



[JUTY 



upper is rough, from portions of the large shells which project from it. 

 On breaking up one of these masses, it was found to contain entire 

 iJnios, many of them having the valves connected and closed, or 

 partially open ; the interior being filled with the same chert, spot' 

 ted with fragments of shells, minute univalves, and fine specimens, 

 of the two species of Cypris, which occur so abundantly. Some parts of 

 the rock exhibit a mixture of sand, cla}^, and fragments of shells, of 

 very moderate hardness ; but the greater portion consists of chert, the 

 materials of which are occasionally arranged in a beautiful, light blue, 

 enamel-like substance, around irregular cavities containing crystals of 

 purple quartz. Some portions also exhibit a minute vesicular structure ; 

 and the whole appearance of this beautiful rock forcibly impresses the 

 mind with the conviction, that it owes its present appearance to the 

 action of the great basaltic eruption, which has enveloped it and the 

 organic remains. The greater number of the shells are converted into 

 chert, but a few retain their original structure ; and in some instances 

 the calcareous matter has been converted into crystals of calcareous 

 spar. Many internal casts of entire shells are found in the substance of 

 the rock, to which they are united at a few points only, a greater or less 

 space being left unoccupied ; in others, the entire shell is converted into 

 siliceous matter, retaining the appearance even of the ligaments unalter- 

 ed ; and fortunately, in a few cases, the hinge and teeth are excellently 

 preserved. 



Numerous fragments of shelly rock, differing much in appearance, lay 

 scattered about over the table-land ; consisting partly of a fine blood-red 

 chert, like that above described, and containing the same shells. The 

 gray chert was more sparingly distributed, and the Unios did not occur 

 in the other fragments. Some of them, composed of a tough white 

 clayey stone, so soft as to soil the fingers, contained Physae, Paludinae, 

 and Limneae, mostly converted into calcedony, but others also retained 

 their original structure, and effervesced with acids. Portions of charred 

 vegetable matter, resembling small fragments of grasses and reeds, oc- 

 curred in these and the harder cherts. Other specimens are composed 

 of a greenish blue crystalline mass, resembling an ore of copper, (but it 

 is of low specific gravity, and contains no trace of that metal,) and the 

 shells contained in them are converted into the most beautiful crystal- 

 line quartz, retaining the form of every convolution of the Physse and 

 Paludinae. The cells of this stone are often coated with fine si ky 

 crystals. Masses of a hard coarse chert, consist almost entirely of 

 Gyrogonites, but contain many of the same Physae and Paludinae. This 

 rock appears to have formed beds of about half a foot in thickness ; but 



