118 



Mr. Brtce on the Geological Structure of Roseneath. 



It is here divided into columns of spheroids perpendicular to the sides of 

 the dike, and separated from one another by imperfect joints. Sometimes 

 each joint is composed of a single spheroid ; one was noticed measuring 15 

 inches by 10; in other cases numerous small closely packed spheroids 

 make up a joint. Instead of a distinct separation as in basaltic pillars, 

 the columns are connected by narrow seams of decomposed greenstone. 

 The columnar structure is here seen in the act of development — if the 

 heat had parted more gradually, a fa9ade of pillars would have been 

 the result. See the remarkable experiments of Mr. Gregory Watt on 

 fused basalt, (Phil. Trans. 1804) of which this spot affords an excellent 

 illustration. 



It wiU appear from the foregoing statements, that the small area we 

 have been describing, is one of considerable interest, exhibiting, as it does, 

 the rare association of many species of erupted rocks in connection with 

 the primary strata ; and affording illustration of some curious questions 

 in theoretical geology. 



c. Limestone, 



8. At a place called the Cove, in the townland of North Alley, on the 

 shore of Loch Long, a bed of limestone is interstratified with the clay 

 slate. It has been originally six or seven yards wide, and has extended 

 eastwards across the low ground between the shore and the cliff, into the 

 cliff itself, and probably much further inland ; but it cannot be satisfac- 

 torily traced. The part next the shore has been almost entirely removed 

 by quarrying ; but from portions which are found among the slate — as in 

 the annexed sketch. No. 5, a vertical i>ection — there can be no doubt of 

 the true position of the bed. 



5 



a a Inclined strata of clay slate. 



b Bed of limestone, 

 of shingle. 



c Bay with accumulations 



The limestone is impure, from intermixture with slaty laminae ; the 

 prevailing colour is bluish gray ; it contains much calcareous spar ; and, 

 like the slate, is destitute of fossils. 



In the new statistical account of the parish of Row adjoining, beds of 

 limestone are stated to occur in the slate rocks of Glenfruin ; these are 

 most probably similar to the bed now mentioned. 



d. Old Red Sandstone. 

 9. The junction of the slate and sandstone is strikingly marked on 



