272 



larly under the summit of the mountain that the plane of the dip was 

 lower than a horizontal plane passing through the same place ; this 

 third item was added to the difference of height, made out hy sub- 

 tracting the height of the chalk from the height of the summit, and 

 the result was taken as the thickness of the basalt. 



It is not pretended that the thickness of the basalt at every locality 

 is strictly accurate. Owing to the faults and downthrows we see to exist 

 in the chalk in every direction, as well as the occasional change where 

 the direction of the dip does not aim at the mountain summit, there 

 was necessarily some modification as to the quantity of the angle. This 

 latter case seldom happened, and it is hoped the thicknesses are pretty 

 correct. 



It will be observed by inspection of this table, and comparing the 

 Antrim outcrop on the east side from the station Wo. 1 to No. 20, with 

 the Deny outcrop on the west from No. 39 to No. 47, that in the east- 

 ern outcrop the chalk is three or four times as thick as it is on the 

 west. The greatest thickness at station No. 5, the "White rock, and No. 

 13, Glenarm in Antrim, is 130 and 170 feet respectively, while the 

 greatest in Derry, at Keady, No. 46, is 33 feet, and at Umbra, No. 48, 

 is 50 feet. In fact it grows thinner rapidly as it proceeds to the west — 

 a physical defect, I am sorry to say, that affects our coal-measures in 

 Ireland, as compared with England, as well as our chalk. 



In the foregoing Table there is no room for some necessary details 

 regarding the localities selected. I deem it therefore necessary to 

 make a few observations on the outcrop of the chalk ; and in doing so, 

 to avoid returning again and again to the same place, I shall note any 

 peculiarity worthy of remark, regarding the rocks in contact with the 

 chalk above and below — that is the basalt, and the greensand, as well 

 as the chalk itself. I shall follow the order of the numbers in the 

 Table. 



1. At Clare, near Moira, the thickness of the chalk in the quarry is 

 52 feet, and the overseer says there are 10 feet more under them to 

 the mulatto or greensand, which they came to in another part of the 

 quarry, making the whole thickness 62 feet. There is no trap on the 

 chalk here, and it may be inferred from the dip, and the ground rising 

 to the north towards the town, that there may be a further accumu- 

 lation of the beds to the north, under the coat of drift which is 20 feet 

 thick. If this be so, the thickness of the chalk here is greater than 

 what I have given in the Table. 



Paramoudras, or supposed fossil sponges of large size — say from 20 

 inches to 2 feet high, and about 15 inches in diameter — occur here rather 

 plentifully. It has been said that they are found in vertical rows, one 

 over the other, in the quarry, but it is not so. I saw two specimens 

 together in this position, in the perpendicular face of the quarry, where 

 there was room for many ; but, as a general rule, they are disseminated 

 without any regular order — often three or four yards assunder. There 

 are two or three trap dykes in the quarry, and as usual the chalk is 

 altered in immediate contact with them — sometimes made yellowish, 



