Rocky Mountains. 411 



At Cape Girardeau, in the country a few nriiles in the rear 

 of Herculaneum and St. cienevieve, and in many places 

 throughout the district of the lead mines, a coarse crystaUme 

 limestone of a light gray colour, occurs, and is usually the 

 lowest rock visible in those places. It is very indistinctly 

 stratified, and has in many respects a manifest resemblance 

 to the more crystalline varieties of primitive limestone. For 

 such it appears to have been mistaken by Mr. Schoolcraft, 

 who, in his work on the lead mines asserts, that the " mineral 

 soil at Mine a Burton, and the numerous mines in its vici- 

 nity reposes on primitive limestone," p. 108. Afterwards, at p. 

 liy, speaking of this primitive limestone, he says, " on go- 

 ing deeper, the rock again graduated into a compact lime- 

 stone, very hard, and of a bluish-gray colour, in which were 

 frequently found small cavities studded over with minute 

 pyramids of limpid quartz;" and again, at the page first re- 

 ferred to, he informs us, " the pnrmtive limeatone passes 

 into transition and secondary in various places on the banks 

 of the Mississippi, between Cape Girardeau and St. Louis." 

 We adduce these statements as confirming our own obser- 

 vation of the alternation of the crystalline or sparry limestone 

 with the compact blue variety. 



We have never met with limestone about the Lead Mines 

 which did not contain organic remains, and the white crys- 

 talline variety abounds particularly in casts of encrinites, 



lobe is far less distinct, and the shell is far more narrowed towards the 

 hinge, and is somewhat less dilated, and much more like an ostrea. It 

 may be called G. corrugata; small valve flat, and very much wrinkled, and 

 like the other, narrowed near the hinge; the beak is short, and curved up- 

 wards and laterally, and the sulcus is very distinct. Length and greatest 

 breadth of the small valve nearly equal, from 1 1-2 inches to 2 inches; 

 found by Mr. Nuttall on Red river. It is in a very perfect state of pre- 

 servation. 



Mr. Nuttall brought also from Red river, a species of ostrea, which to 

 the eye appears hardly changed. The anterior portions of the specimens 

 are wanting, but the greatest breadth of the remaining portion of the lar- 

 gest one is nearly three inches. The hinge fosse in this species is propor- 

 tionally much more contracted and smaller in every respect, than any 

 other species of the genus we have seen. That of the specimen above 

 mentioned, is less than 1-2 an inch. The specimens were evidently those 

 of old shells being much thickened. 



Another species of ostrea, a hinge fragment of an old and thickened in- 

 dividual, which appears to have been long and narrow; the hinge fosse it- 

 self is long and wide. 



Length of the hinge more than 3 inches, greatest width, do. 1 inch. 



Sat 



