164 Microscopic Structure of Canadian LimestGnes. 



thin transparent film. A low power is sufficient to show the 

 general forms and nature of the fragments, but they are often so 

 beautifully preserved as to display their most minute structures 

 when examined with high powers. 



With the view of ascertaining whether there is any difference 

 of material in different parts of the beds,. I selected from one of the 

 quarries, containing two thick beds with some intervening and 

 overlying thin shaly layers, specimens representing the overlying 

 shaly limestone, the material between the two beds, and the upper, 

 middle, and lower portions of ea;di bed. Duplicate preparations 

 of all these specimens were kindly male for me by Mr. E. Murphy, 

 of this city; and on being examined they afforded the following 

 results : — 



1. Above upper bed.— -Very small fragments of crinoids and shells with 



numerous minute and probably young uni- 

 valve and bivalve shells, in patches in a 

 paste containing black earthy and organic 

 matter. 



2. Upper part of bed A.— Principally joints of crinoids ; some fragments 



of corals, especially Ptilodictya and Monti- 

 culipora, and shells. 



3. Middle of Bed A.— -Similar to the last but more corals. 



4. Bottom of bed A. — A still greater proportion of Ptilodictya and 



Monticulipora. 



5. Between A. & B. — Crinoids and Monticulipora in about equal pro- 



portions, some Ptilodictya. 



6. Upper part of bed B. — Similar to last, but still more corals. 



7. Middle of B. — Principally Monticulipora and Ptilodictya, but still 



many crinoids. 



8. Bottom of B.— Almost wholly Monticulipora and Ptilodictya. 



It thus appears that the only material difference in these speci- 

 mens is the great prevalence of crinoids toward the top, and of 

 corals and Polyzoa toward the bottom. It is proper to add that f 

 though the families and genera named above largely predomi- 

 nate, there may be detected in any specimen fragments of shells 

 of brachiopods and gasteropods, and of corals of other genera 

 than those named, though in comparatively small quantity.* 

 With the exception of the first specimen, none exhibited more 

 than traces of earthy or aernaceous matter. 



The fine grained earthy limestone, marked No. 1, and which, 



* According to Mr. Billings, Cystideans have also been important 

 contributors ; but in my examinations their remains are not distinguished 

 from those of the Crinoids. 



