Vol. 65.] THE CARBONIFEROUS LIMESTONE OF COUNTY CLARE. 541 



The large area of country dealt with, and the impracticability 

 of working, in detail, sections many miles in length, have rendered 

 it impossible to study carefully the evolution of any one group 

 of organisms ; but, if connecting links have been found which can 

 be added to the rapidly lengthening chain of our knowledge of 

 the t'aunal development during Avonian time, one of the objects 

 of this paper will have been partly realized. My primary object, 

 however, being to test the value of the generally accepted Carboni- 

 ferous zone-fossils, in working the rocks of more distant regions 

 than those already dealt with, I have not deemed it advisable to 

 overburden the somewhat extensive list of fossils which now 

 exists, by a description of any new or rare species which is not of 

 practical use for zonal purposes. 



II. Sequence of the Deposits. 



The accompanying table (p. 542) illustrates the relation between 

 the palseontological zones and the former strati graphical divisions of 

 the Geological Survey. 



The vertical thicknesses, which show a considerable variation 

 throughout the county, are taken from the Survey Memoirs ; they 

 can only be considered approximate, owing to the absence of clear 

 measurable sections. The great thickness of the Upper Limestone, 

 of which nearly 1500 feet must be assigned to the Dibunophyllimi- 

 Zone, finds a parallel in the Midland area of Derbyshire and 

 Staffordshire. 



III. Nature and Extent of the Outcrop, and 

 Topographical Features. 



The Carboniferous Limestone floors nearly the whole of Eastern 

 Clare, from the southern shore of Galway Bay to the banks of the 

 Shannon. This area, for the purposes of description, may be con- 

 veniently divided into a northern district comprising the baronies 

 of Burren and Inchiquin, and a southern district comprising those of 

 North and South Bunratty and North and South Tulla. 



Nearly the whole of the northern district is formed by a vast 

 elevated plateau of Upper Limestone, with a surface of bare rock 

 many square miles in extent, practically devoid of vegetation. The 

 beds, though slightly undulating, have an average dip of about 2° to 

 the south and south-west, in which direction they pass beneath the 

 Coal Measures. On the south and east, however, they end abruptly 

 in steep escarpments with terraced sides ; these great limestone- 

 terraces can be traced for mile after mile across the country, and 

 their formation by subaerial agencies is a point of considerable 

 geological interest. 



They are, I consider, primarily due to the influence of jointing, 

 and the alternation of coarse and fine bedding and their unequal 



