1893.] NEW-YORK MICROSCOPICAL SOCIETY. 15 



thing of structural interest even on casual examination, and they 

 are likewise well adapted to making very fine thin rock sections. 

 This gravel is brought from near Leadbetter, Lee Co., Texas, not 

 far from the Colorado River, and the bulk of the gravel is of a 

 flinty nature, seeming to be of calcareous fossil strata, altered 

 through silicification. 



" I have sent, with the fossil wood, a specimen of oolitic and 

 foraminiferal flint, nearly equal in translucency to the chalk flints 

 of the British coast, which can be taken as a type of the flinty 

 gravel of the Colorado River basin. 



" In another package I have sent five specimens of a cretaceous 

 or calcareous gravel from San Antonio, Texas, where it is exten- 

 sively used in the park walks and the pavements around the city. 

 Most of this gravel is in the shape of ovoid or spherical balls, and, 

 if broken in two, are found to be composed of concentric, spher- 

 ical, concretionary layers, that may be detached continually until 

 the central core, or nucleus, is found. In the specimens sent I 

 have polished each face, to show the peculiar crystalline deposit, 

 from the central nucleus to the outer margin. The two larger 

 pieces are from the one original, and may be fitted together to 

 illustrate the ovoid shape. Inspection suggests that thin sec- 

 tions, when examined with the polariscope, would give concentric 

 radial color effects, which would prove quite interesting. I 

 noticed that children in San Antonio played with them as mar- 

 bles, using, of course, the roundest that could be found. 



"These gravel specimens possibly illustrate a recomposition 

 product of calcareous strata, as in limestone caves, and then, while 

 in solution, redepositing upon some granule or fragment as a 

 nucleus, and gradually augmenting by the same law of calcareous 

 deposition indefinitely, as the balls vary from very small to very 

 large, in the general mass of gravel as distributed. Single and 

 double centres of concretionary action may be noted in the seve- 

 ral specimens." 



OBJECTS EXHIBITED. 



1. Micrococcus pneujnonicus Friedlander, under a Zeiss one- 

 twelfth homogeneous immersion lens: by Charles S. Shultz. 



2. Bacillus tuberculosis, under a Spencer one-tenth homogeneous 

 immersion lens : by Charles S. Shultz. 



3. Comma bacillus, X 900 : by Louis Heitzmann. 



