1809-1910.] 2KK 



Chalk." The rock from the " neck " was found to be a fine- 

 grained ophitic dolerite, one of the typical igneous rocks of the 

 district. The " dyke " proved to be particularly interesting. It 

 is a granitoid, holo-crystalline basic rock, and may be classed as a 

 " diabase without olivine." Its most striking feature is the 

 beautiful pleochroism of the augite. A sample of the chalk 

 taken two yards from the dyke showed it converted into a 

 typical crystalline limestone, with large crystals of calcite. 

 Adjoining and caught up in the dyke a rock was found which 

 weathers so dark that it was difficult to tell it from the dyke itself. 

 It proved to be the chalk completely altered into a calc-silicate 

 hornstone. The cause of this alteration of the chalk is difficult to 

 ascertain. Mr. Gough concludes that the dyke supplied the 

 heat necessary, and that the metamorphism took place sub- 

 sequently to the formation of the " neck," and suggests that there 

 has been a mixture of the dyke with the chalk in different 

 proportions. On this occasion, however, at another place, some 

 little distance from the dyke, specimens of altered chalk were 

 obtained, which in the hand closely resemble the calc-silicate 

 hornstone, and it is hoped that at some future time the invest- 

 igation may be continued. 



VALLEY OF THE ROE. 



The third excursion took place on Saturday, 26th June, to 

 the Valley of the Roe. Fifty-two members and friends travelled 

 by the 8-25 a.m. train from Belfast, and on reaching Limavady, 

 were met by Mr. H. C. Marshall, one of the Conductors for the 

 day. No time was lost in mounting the cars in waiting, and soon 

 all were on their way to the Dog Leap, 2 miles up the River Roe. 

 No more interesting spot could have been selected for the starling 

 point of the Roe Valley exploration than that known as the Dog 

 Leap, from which, indeed, the town of Limavady derives its name. 



