Distribution of the Rhabdophora, 251 
As a rule, however, the simple occurrence of black shales with 
Graptolites is of itself regarded as affording sufficient evidence 
of the Llandeilo age of the surrounding rocks * * * § ; and this also 
appears to have been the sole reason for the authoritative 
opinion of the Irish Survey that the black graptolitic shales 
of Meath and Down rose in anticlinal lines from below the 
barren Proterozoics of those counties. The marvellous confu¬ 
sion and obscurity that has been the inevitable result of these 
erroneous views is very naively summed up in Mr. Kinahan’s 
admirable 1 Geology of Ireland,’ published within the last few 
months. According to this author the Ordovician (Cambro- 
Silurian) rocks of Ireland are divisible into two successive 
formations :—a lower (Dark shale) series, characterized gene¬ 
rally by fossils of Llandeilo type, associated in some places, 
however, with Caradoc species; and a higher (Ballymoney) 
series, in which the assemblage of fossils “ is to be compared 
with that of the Bala rocks, though Caradoc species are not 
uncommon, while f whenever black shales occur , no matter on 
what horizon , they nearly always contain fossils of Llandeilo 
type 
In Scotland the same floating idea that the simple presence 
of Graptolites in association with black shales affords sufficient 
evidence of the Llandeilo age of the surrounding rocks, has had 
a similar influence. I have already pointed out how it weighed 
with Murchison in his estimate of the geological position of 
the typical Moffat shales themselves. On the subsequent 
discovery of similar black shales in the rocks of the mining 
district of the Leadhills,they were as unhesitatingly assigned to 
the Llandeilo period by the officers of the Geological Survey 
although some of them were known to be actually interstratified 
with beds crowded with Caradoc-Llandovery fossils, and at 
the same time were supposed to be many thousands of feet 
higher in the vertical series than the so-called “ Upper Llan¬ 
deilo ” shales of Moffat. Even as late as 1872 we find similar 
rocks near the Mull of Galloway classed as of indubitable 
Llandeilo age on the evidence of a list of Graptolitic species, 
not one of which has ever been detected in Llandeilo rocks, 
or in any strata whatever lying below the base of the Llando¬ 
very §. Indeed the only palmontological evidence yet adduced 
of the Llandeilo age of the rocks of the Southern Uplands is 
the mere presence of Graptolites in seams of black shales. 
* Baily, ‘ Graptolites of Meath,’ &c., Geol. Sue. Dublin, 18(52 ; and 
Quart. Journ. Geol. Soc. London, 1869, pp. 158-102. 
t Kinahan, ‘ Geology of Ireland,’ 1878, pp. 24,25. 
\ Memoirs Geol. Surv. Scotland, Explan. Sheet xv. p. 18. 
§ Ibid. Sheet i. 1872, p. 7 and Appendix. 
