380 ME. E. WETHERED ON THE DEVONIAN" 



broken. Among them are portions of coral and joints of 

 crinoids. 



No. 3 also shows very fragmentary calcareous objects, with in- 

 filling calcite. Ossicles of crinoids can be distinguished. 



No. 4. At the top of the quarry occur beds representative of the 

 Goniatite Limestone which Mr. Ussher ^ considers to be of Upper 

 Devonian age. 



The specimens collected as typical of this limestone show it to 

 be quite different in structure from the beds below. There is a fine 

 crystalline groundmass in which are several fragmentary remains 

 of organisms. One of these appears to be a foraminifer, and it is 

 especially interesting as being the only one found in my slides of 

 the South Devon Limestones. The Goniatite Limestone seems to 

 have been formed by an accumulation of small shells, foraminifera, 

 &c., which have been filled in with a fine calcareous mud. 



§ 3. CONCLTTSIONS DEAWN FEOM EXAMINATION OF THE SlIDES. 



The microscopic examination of the Devonian Limestones is not 

 very satisfactory so far as structure is concerned. There is, indeed, 

 ample evidence that these limestones have been built up by the 

 calcareous remains of organisms, but the outlines of structure have, 

 for the most part, been obliterated by molecular changes. These 

 South Devon limestones are, therefore, a proof that by such changes 

 the structure of the calcareous organisms, of which they are mainly 

 formed, can be rendered indistinguishable, and the rock become 

 entirely crystalline. 



It is well known that in more recent limestones the interstices of 

 the constituent organisms are generally occupied by a quantity of 

 calcite. This is also the case with such Devonian Limestones as I 

 have examined. In the best preserved types the calcite can easily 

 be recognized by its large clear crystals. On the other hand, the 

 altered portion of the limestone is represented by small crystals in 

 aggregates, and these are usually stained by iron oxides. 



So far as the evidence warrants a conclusion being drawn, the 

 Devonian Limestones of South Devon appear to have chiefly origi- 

 nated from corals, crinoids, ostracoda, stroniatoporoids, and frag- 

 ments of shell ; while the Goniatite Limestone alone contains fora- 

 minifera. 



The Coomb End Limestone is almost entirely made up of coral; 

 indeed, it appears to represent an ancient coral-reef. 



Some of the beds at Hope's Nose and Daddy Hole are almost 

 entirely of coralline origin, but differ from those at Coomb End in 

 that they represent accumulations of coral debris. 



The question may now be fairly asked, what makes the De- 

 vonian Limestones of South Devon so crystalline ? Mr. Ussher, 

 quoting the remarks of Prof. H. S. Williams, of Ithaca, N. T., says 

 that " in South Devonshire the rocks are greatly disturbed, broken 

 by faults, standing at various angles, folded and distorted ; eruptive 

 1 Quart. Journ. Geol. Soc. vol. xlvi. (1890) p. 507. 



