CLASSIFICATION OF REEF LIMESTOXES 349 



For the clastic limestones here discussed the names calcirudiie, cal- 

 carenite, and calcilutite are proposed.* They may be defined as follows: 



CALCIRVDITE 



(Etymology : calx = lime + rudus = rubble) 



A limestone or dolomite composed of broken or worn fragments of 

 coral or shells or of limestone fragments, the interstices filled with lime 

 sand or mud and with a lime cement. It corresponds to psephite 

 among the siliceous rocks. 



Some of the varieties of calcirudite are : 



1. Coral breccia. 



2. Coral conglomerate. 



3. Shell breccia. 



4. Shell conglomerate. 



5. Limestone breccia. 



6. Limestone conglomerate. 



The last two well known varieties must be included under the term 

 calcirudite, even though they are made up of old sedimentary limestones 

 which have been broken and recemented. 



Stratification is more or less marked in calcirudites, as it is in other 

 coarsely fragmental rocks. On the one hand they grade into the unworn 

 organic deposits or into the solid limestone beds, and on the other into 

 the members of the next division. 



CALCARENITE 



(Etymology: calx = lime -f arena = sand) 



A limestone or dolomite composed of coral or shell sand or of lime 

 sand derived from the erosion of older limestones. In structure it re- 

 sembles psammites or siliceous sandstones, being generally knowm by 

 the term sandstone. Stratification is well marked, and the rock not in- 

 frequently shows cross-bedding structure, as noted among the dolomitic 

 calcarenites of the Niagara gorge.f Ripple marks have also been noted 

 in some impure fine grained calcarenites of the Traverse group of Michi- 

 gan.J Calcarenites constitute the main mass of the limestones of the 

 Traverse group of Michigan, of the Onondaga of southeastern Michigan 

 and western New York, and of the Niagaran beds of southeastern Wis- 

 consin. INIuch of the Lockport limestone of western New York is a cal- 

 carenite, and, in fact, so far as my observations go, a large proportion of 



*I am indebted to Professor Wm. ^'orth Rice for suggestions regarding the orthography of 

 these terms, 

 t A. W. Grabau : Guide to Geol. and Pal. of Niagara Falls, pp. 107, 108. 

 JGrabau : Ann. Rep. Geol. Surv. 3Iich,, 1901, p. 209. 



