196 THE AMERICAN MONTHLY [July, 



anchors, shields and wheel plates of carbonate of lime, 

 in a number of rosette preparations in my possession 

 have been gradually dissolved awaj in the' balsam leav 

 ing the merest traces of their former outlines after eight 

 •years of inclusion in the slides, which shows that the 

 beautiful and expensive rosette preparations of this char- 

 acter are not durable or permanent. 



The sponge and other spicules, anchors, shield and 

 wheel plates, Echini, etc., of the Mississippi marl are all 

 polariscope objects, and the stellate spicules by them- 

 selves act as analyzers, independent of the nicol prism 

 being placed above the slide to develop the color effects. 



I have prepared to accompany this paper a plate or 

 sketch, with numbers and names of the objects illustrat- 

 ing the various interesting fossil bodies of microscopic 

 interest found in this American calcareous marl deposit 

 in the hope that it may add interest to the perusal of the 

 text. It appropriately transpires in conjunction with 

 this subject that in " Carpenter on the Microscope " 

 there appears a plate containing a somewhat similar 

 showing of micro-organic remains derived from the 

 white mud of the Levant, or from the harbors of the 

 Eastern end of the Mediterranean Sea. 



The circular scales or plates indicated by the figure 

 numbered 2 in plate, polarize with brilliancy and sug- 

 gest the circular crystals of Salicine. The marine calca- 

 reous marl stratum offering this variety of interesting 

 objects is distant from the Gulf of Mexico, eighty miles 

 in a northerly direction, and the surface or superficial 

 formation covering the marl area from that point to the 

 Grulf is known as the Lafayette formation, which consists 

 of silicious sands and quartz pebbles without any ma- 

 rine fossils, but fossils of petrified vegetation alone, 

 chiefly of the Coniferae. 



