194 Dr. Berger on the Geological Features 



The penetration of the wood by the siliceous matter is sometimes 

 compleat ; sometimes one extremity of the same fragment is thus 

 petrified \A,^hile the other remains in a ligneous state. The oak, the 

 holly, and the hazel appear to have been the trees thus affected. 



A phenomenon occurring in some caverns near the Black Rock, 

 on the south of Church Bay in the isle of Rathlin, may be properly 

 referred to this article. 



These caverns (four in number) although excavated in the ba- 

 saltic rock and at a point remote from any calcareous formation, are 

 yet invested with calcareous stalactites, depending from their roofs, 

 and by their droppings upon the floor depositing a crust of about an 

 inch in thickness. 



This circumstance appears worthy of attention, since the calca- 

 reous matter seems evidently, from the situation of the caverns, 

 to have been derived from that which enters as a chemical ingre- 

 dient into the composition of the basaltic rock, separated from the 

 mass and deposited in its present situation by the percolation of 

 water which the rain or springs must have furnished. 



It proves therefore the permeability of basalt which has sometimes 

 been denied, and gives countenance to the opinions of those who 

 consider the nodules of calcareous spar and zeolite, occurring in the 

 amygdaloidal varieties, as the results of an infiltration which has gra- 

 dually filled up what were once vesicular cavities ; it is remarkable 

 that the substances so occuiTing are such as the chemical constitution 

 of the matrix would qualify it to afford by a similar process ; and in 

 the instances above described, that very process may be detected 

 passing under our immediate observation. 



A vesicular variety of basalt, of which the pores contain water, 

 occurs at Ballylaglan on the north of Coleraine. Dr. Richardson 

 has mentioned it as a proof of the aqueous origin of basalt, believing 



