VOLCANIC PIPES 365 



that the rock may have been a melilite-basalt, melilite 

 being a mineral that is very prone to alteration ; it has 

 already been remarked that the character of those 

 portions of kimberlite which are free from inclusions 

 certainly favour such a view. 



It is most interesting therefore to find that dykes of 

 a rock indistinguishable from kimberlite have been found 

 at two localities in North America, at Syracuse (New 

 York) and in Elliot County (Kentucky), 1 and that in 

 two dykes from the former locality melilite has been 

 identified. 2 The intrusions contained in places numer- 

 ous inclusions of sedimentary rocks and fragments of 

 granite. 



Lately several interesting dykes have been found in 

 Prieska and Britstown which belong to the ultrabasic 

 group of the lamprophyres ; some contain abundant 

 biotite, others augite and aegerine, while one has a base 

 composed of analcime and is therefore very closely allied 

 to the rock known as monchiquite. Fragments of 

 lamprophyres of similar types have also been found in 

 fissures and pipes containing kimberlite. 



Although all these occurrences differ much in character 

 and some varieties are occasionally found to be cut by 

 others, there can be no doubt that they all belong to 

 one period of volcanic activity. No direct evidence of 

 their age is obtainable, but, as already mentioned, they 

 are later than the Karroo dolerites ; this is not only the 

 case with the kimberlite pipes but with the Matjesfontein 



1 Carvill Lewis, p. 58. 



2 Smyth, Am. Journ. Sci., xiv., 1902, p. 29. 



