37 [ 237 J 



sent me by Lieut. Barry ; and I would sooner have acknowledged their 

 reception, had I not hoped for the pleasure of an interview with you at 

 Wasliington. * * * * The specimens are exceedingly in- 

 teresting. I found, in two of the specimens of calcareous marl, precisely 

 the same microscopic multilocular shells 1 had previously detected in lime- 

 stones from the cretaceous group of New Jersey. These shells resemble 

 small nautili, and belong to iheforaminifera of D'Aubigny. Great inter- 

 est will be fflt to belong to these American localities, h-om their connexion 

 with the wonderful discoveries of Ehrenberof, who has shown that these 

 minute shells (called by him poli/thalamia) constitute a large portion of 

 chalk, marl, (fee ; and the sandy deserts of Africa are often only a moving 

 mass of these beautiful little organisms. (See the I.ond. and Ed. PhiL 

 Journal, May and June, 1841.)" 



3d. The bed C, composed of a foliated and selenitous clay, acquires 

 interest, as it develops itself in other localities. Its thickness is variable. 

 I have found it 20 feet thick ; and its strata are divided by thin layers of a 

 more indurated white clay. In these several stages, the scleniferous clay, 

 of a yellowish color at the bottom, becomes black and more foliated in its 

 superior beds. The selenite is more abundant; replacing, as it were, the 

 white indurated clay. 



The specimens of selenite obtained from this division of the Dixoa 

 group are worthy of notice, in consequence of the peculiar forms that they 

 assume — some of them presenting the appearance of leaves of trees, beau- 

 tifully and gracefully scolloped; which has encouraged me to venture upon 

 a descriptive name as a mineralogical variety by which to designate them. 

 I call them phylloidal selenite. Others are in the usual shape of six sided 

 regular prisms, " en fer de lance^^ lanciform, radiating, tfec. I have had 

 designs executed of these, among the newest of these forms, that might in- 

 ter(!St the mineralogist. But these, as well as other drawings of fossils, 

 cannot, in the nature of circumstances, find a representation in the present 

 report. 



4ih. The rock desiiznated as D is the last member of the trans Mississip- 

 pian cretacious formation, as it presents itself on the Missouri river: it is a 

 vast deposite of plastic clay, about 2lOO feet thick, which may be considered, 

 however, divided into two equal parts by a stratum of argillaceous carbo- 

 nate of lime in nodules, of which I had no occasion to ascertain the thick- 

 ness. Many of these nodules, having fallen from their origiaal position, 

 are met with in considerable quantities in the beds of the ravines, and in 

 other places. It is known that this variety of iron ore is among the best. 

 Associated with it is a ferruginous sandstone, which presents itself in flat 

 polygons, on the surface of which there are seen numerous concentric lines 

 of great regularity, so as to imitate the transverse sections of a tree. The 

 same deposite contains, disse ninated through it, lumps of the yellowish 

 clay of the inferior stratum C, and enclosing leaves of selenite, and cavi- 

 ties lined with concretionary gypsum. But these lumps are more frequent 

 in the lower half of the deposite than in the upper, and finally cease alto- 

 gether to appear. 



There are also found, throughout the clay deposite, loose pieces of lime- 

 stone, the origin of which I will not attempt to assign precisely ; though 

 they may have belonged to subordinate beds of this rock, that exist 

 somewhere in this formation. I have collected some myself; others were 

 brought to me by my men ; and, as a notification to future geologists who 



