312 APPENDIX 



which Mr. Matthew has presented a fine slab to 

 the Museum. I have also, through the kindness 

 of Professor Winchell, been enabled to compare 

 these with his Crypt ozoon Minnesotense^ and Dr. 

 Walcott has added specimens of his Stromatoporoid 

 forms from the pre-Cambrian beds of Arizona. It 

 would appear from these and other specimens in 

 our collections from the Cambrian and older 

 Ordovician beds, that we have here an ancient type 

 of Stromatoporoid organism in which the original 

 laminae seem to have been thin and coriaceous, 

 without apparent pores or pillars connecting them 

 with each other, but having between them relatively- 

 thick layers of fine fragmental matter penetrated by 

 numerous irregularly tortuous and branching tubes. 

 The laminae often present a carbonaceous or 

 chitinous appearance, though frequently replaced by 

 mineral matter, and the intervening layers show 

 both a calcareous and carbonaceous substance, with 

 much fine silicious sand often as rounded grains, 

 and apparently some dolomitic granules. The 

 tubules seem destitute of any distinct wall, other- 

 wise the whole would resemble on a large scale the 

 nodular and laminated masses of Girvanella, which 

 Wethered has described as surrounding organic 



