402 Mr. Weaver on the Structure of the South of Ireland, 



swered by extended researches; and until these be completed, 

 it may be prudent to defer the assignment of the older strati- 

 fied formations of Devon and Cornwall to a precise period 

 in respect of relative age. 



In the limestone bands of the south of Ireland I have shown 

 that 50 species of fossils have been determined with precision, 

 that is, including Leptmia depressa and Leptana lata ; but 

 others also occur which have not been determined, e. g., Avi- 

 cida and Goniatites. Of the fifty species, six are peculiar ; 

 twenty-six common to other transition tracts at home and 

 abroad (of which twelve occur in the Eifel); v^hWe forty -three 

 of the species are common to the carboniferous limestone 

 also*; thus nearly agreeing with the numbers of a correspond- 

 ing character found in Devon and Cornwall, and in the Eifel. 

 But as in the south of Ireland, neither the bands of limestone, 

 nor the strata with which they are directly associated, nor 

 yet those situated more north which lie deeper in the series, 

 have hitherto undergone that rigid examination which is re- 

 quisite with respect to the organic remains which they may 

 contain, we are not authorized as yet to pronounce upon the 

 precise proportions in which those fossils may exist relatively 

 to each other in the general series. Yet enough has already 

 been elicited to prove that those limestone bands stand in un- 

 interrupted connexion with strata in which fossils of a more 

 decided transition character are bv no means wanting ; and 

 no sufficient evidence has yet been produced to invalidate the 

 conclusion that the whole constitute together one consecutive 

 series, notwithstanding we may perceive some distinctions 

 between the fossils of the schistose and greywacke strata and 

 those of the included bands of limestone. Continued re- 

 searches will doubtless throw further light on this subject. 



A pertinent observation of Professor Sedgwick may here 

 be aptly introduced : " There are two elements of classifica- 

 tion applicable to stratified rocks of all ages, namely, phy- 

 sical structure and order of superposition; one giving the 

 mineral ogical unity of a group of rocks, the other their relative 

 age. In addition to the two former, are classifications founded 



on the organic remains in the several groups As, however, 



the (so-called) laws respecting the distribution of organic 



* See Memoir on the South of Ireland in Geological Transactions, vol. v., 

 second series, and Lend, and Edin. Phil. Mag. for August 1839. When the 

 former work was finished in 1835, I considered the Isocardia oblonga as 

 peculiar to the Cork band of limestone; but Professor Phillips's Illustra- 

 tions of Yorkshire, part ii., published in 1836, have shown that the Iso- 

 cardia oblonga occurs also in carboniferous limestone in Yorkshire, and in 

 the counties of Kildare and Dublin. 



