TRANSACTIONS OF THE SECTIONS. 99 



Carboniferous limestone, and it usually presented an vuidulating surface wliicli 

 occasionally affected the form of elongated elliptical liills, which usually ran 

 parallel to each other. This fact was especially exemplified by Clew Bay, situated 

 on the west coast, in which were upwards of 300 islands, the surface of which 

 was composed of boulder-drift resting on Carboniferous limestone. He mentioned 

 that at least on the eastern the boulder drift had a thickness of about 100 feet, but 

 probably was much thicker towards the west. He described the boulder-drift as 

 composed of a base of sandy or gravellj^ clay, which contained numerous rolled 

 masses, huddled together in a confused manner without reference to size, and that 

 their dimensions ranged between those of a small egg and two or three cubic feet iu 

 diameter. He next adverted to those remarkable ranges of hill, which varied in height 

 above the surface of the boulder-drift from twenty to sixty feet, the ascent being 

 usually about thirty degrees on the west side, but less steep on the east. These 

 Esker hills were very numerous in the midland plain, especially in the coimties of 

 Mayo, Galway, and Roscommon, on the west side of the Shannon, and of the King's 

 County and Westmeath on the east. Their general direction was from west to 

 east ; and one great Esker, which extended from west to east from the county of 

 Galway to Westmeath, was used as the post road from Dublin to Galway, for a 

 length of 30 miles. This great Esker crossed the river Shannon at Athlone, and 

 was subsequently cut through by it, exhibiting a great shoal at the present time, 

 on which the old bridge of Athlone was built. On the western side, about 50 feet 

 above the river, an ancient fort had been erected to defend the passage, and this 

 fort still remained in perfect preservation. The town of Athlone was also built 

 on the east side of it, and extended from thence nearly 20 miles. Fifteen miles to 

 the south of Athlone, the river Shannon was crossed again by another Esker, also 

 running from west to east, and in this place the Esker presented very steep 

 acclivities on either side. He last described a very remarkable Esker called the 

 " Horseshoe," from its form, the north arm of which running eastward extended 

 for 10 miles, whilst the southern extended 8 miles, leaving an opening of 8 miles, 

 ■with the town of Clara in the centre. The slopes of these horseshoe Eskers on 

 the west side were steep, ha\'ing an angle of about 30°, while on the outer side the 

 slope was only fi-om 10 to 15°. Having mentioned that in many cases Eskera 

 were observed, particularly to the west of Athlone, having- a north and south 

 direction, he gave it as his opinion that the Eskers were deposited on the top of 

 the boulder-drift at a subsequent period, and that the materials, which were 

 similar to the boulder-drift, with the exception of the admixtiu'e of sandy clay 

 matter, were deposited from currents and waves in a shallow troubled sea, and 

 possibly did not owe their existence to glacial action. Sir Richard next directed 

 the attention of the Section to the occun-ence of large erratic blocks, totally uncon- 

 nected with the gi-avel, which were found resting on the sm-face throuo-'hout the 

 entire district, from Galway Bay in an eastern and southei'n direction, passing over 

 the summits of the Sli eve-bloom mountains, near Roscrea, and extending from 

 thence through the King's and Queen's counties. These blocks were all composed 

 of a peculiar porphyritic granite fi'om the district situated to the north of Galway 

 Bay. This granite was composed of red and white felspar, gTey quartz and black 

 mica, and contained numerous crystals of red felspar, which rendered the appear- 

 ance so peculiar that no dotibt could be entertained that the granite blocks ju)ove 

 mentioned were derived from the Galway district. 



These blocks are usually angular though occasionally slightly rounded. One, 

 whose dimensions was 10' by 5' by 3', equal to 4 tons in weight, is described by 

 Mr. Joseph O'Kelly, of the Geological Survey of Ireland, as resting on Lower 

 SUurian gi-oimd, 10 miles to the north of the Town of Roscrea, at an elevation 

 exceeding 1000 feet above the sea ; and his colleague, Mr. G. Henry Kinahan, the 

 senior geologist, found great numbers of these blocks scattered over the limestone 

 plain, in the neighbourhood of Atheniy, to the east of Galway. He likewise 

 described large blocks of the same granite in the valley of Glensascaul, at the 

 western base of the Slieve-bloom mountains, the dimensions of one of which was 

 12' by 10' by 11', equal to 110 in weight, and others whose weight varied from 

 3.5 to 48 tons. 



Sir Richard next alluded to auother di-Ift of erratic blocks, which took a course 



