26 PROCEEDINGS OF THE NATIONAL MUSEUM vol.76 



A. Analyses of various beds of the Thunder Bay stage show 



Minimum Maximum Average 



SiOj 21. 54 to 55.86 48.43 



FeaOs 4.66 to 5.11 4.89 



AUO3 4. 58 to 201 93 lai 9 



CaCOa 3. 18 to 60. 89 24;. 90 



MgOOa 2. 57 to 5.94 3.70 



B. Analyses of various beds of the Alpema stage give 



Minimum Maximum Average 



Si02 0.20 to 4.62 1.39 



FeaOs .13 to .53 .30 



AI2O3 .13 to 1.79 .75 



CaCOa 89. 20 to 99. 63 96. 69 



MgCOa .21 to 8.61 1.71 



G. Analyses of various beds of the Presque Isle stage give 



Minimum Maximum Average 



Si02 28.38 to 66.39 52.10 



Fe^Os 1.59 to 5.87 3.49 



AI2O3 7. 23 to 20. 44 13. 82 



CaCOa 9. 12 to 33. 00 21.06 



MgCOs .50 to 5.02 2.15 



The foregoing tables make no pretense at completeness of statis- 

 tics, nor are the computed averages of strictly quantitative nature 

 for the entire thickness of any of the stages. They will, however, 

 serve to bring out the strong contrast in the qualitative character of 

 the rock constituents in the three series of beds and explain the 

 restriction of the cement industry to beds belonging to the middle 

 division. 



Distinctive species of the eastern Travet^se. — As with the organic 

 remains of the Traverse Bay section the greater majority of fossils 

 found in the Traverse beds of eastern Michigan have as yet received 

 little or no discriminating attention. A full discussion of the f aunal 

 character of associations in the various portions of the section must 

 await the completion of considerable paleontologic study. Ready 

 means for distinguishing between the broader divisions of the succes- 

 sion is, however, afforded through the restriction of a number of 

 abundant and easily recognized species to one or another of the three 

 stages. So far as known the species mentioned below have not 

 been found elsewhere in the sequence than in beds of the stage under 

 which each is respectively cited. 



Species characteristiG of the Thunder Bay stage 



Stereolasma cf. recta (Hall). 

 Zaphrentis (Homalophyllum) ex^igua (Billings). 

 Pristiphyllum longiseptum Grabau (chironym). 

 Cylind/rophyllum ct. panicum (Winchell). 



