KIMBERLITE PIPES AND INTRUSIVES IN DIATREMES--Massive porphyritic to brecciated 
     intrusive masses and dikes.  Several diatremes contain diamonds, xenoliths of Silurian
     and Ordovician limestones and dolomites, fragments of Precambrian crystalline rocks,
     and xenoliths of peridotite, westerite, and eclogite.