88 LESSONS IN CHEMISTRY. 



of composition which the beds present, they differ very much 

 in value. They are in general loose and porous; and ai*e 

 especially adapted for the cultivation of fruit-trees and deep 

 rooted plants ; occasionally when the silica is in minute grains, 

 and clay forms the cementing material, a moderately cohesive 

 soil is produced. In England the open soils on the old 

 sandstone in Hereford and the neighbouring counties are 

 famous for their orchards, and in this country the best fruit- 

 growing districts of Kilkenny and Limerick are situated on 

 this formation. The new red sandstone may be observed in 

 the valley of the Lagan and also at various points along the 

 coast of Antrim, where it occasionally contains beds of 

 Gypsum (46) and rock-salt. 



128. Limestone I^RjiATiON. — The limestone formation 

 covers but a small space in England and Scotland, but in Ire- 

 land as we have akeady stated, it is largely developed, 

 occupying fully two thirds of the island, and being found in 

 every county with the exception of Wicklow. By the geolo- 

 gist it has been recognised as consisting in this country of three 

 distinct formations or beds. Thefifi_arejQamed from Jh£irj)0si3^ 

 ition the_upper, middle, and lower limestonesr~The lower lime- 

 stoiie forms the prevailing rock of the central counties, and af- 

 fords the fine black marbles of Carlow, Galway, and Kilkenny, 

 as well as the red marbles of Armagh. The middle limestone, 

 which has received the name of Calp^ occurs in the neighbour- 

 hood of Dublin, and consists of a dark limestone, containing 

 a large amount of clay, and not more than 68 per cent of cai'- 

 bonate of lime. The w/^/^er limestone is not found in the 

 central flat country, but in the north is discovered in Sligo, 

 Feraianagh, and Leitrim, and in the south in Tipperary, 

 Carlow, and Kilkenny. If you look at the distribution of the 

 limestone formation, as laid down in the geological map, you 

 will perceive, as has already been stated, that it occupies the 

 great central plain of the island, extending in a straight line 

 from DubUn to the coast of Galway, on the shore of the 

 Atlantic. Its level, however, is frequently disturbed by the 

 protrusion of sandstone rocks, and branches of it may be 

 observed extending a considerable way from the central 

 mass in Donegal and other counties. 



129. In connexion with the limestone formation we may 

 notice a variety of hmestone which is found in a few places in 

 Ireland, and which, from containing a considerable amount of 



