8 * BASALTIC ROCKS, 
Concerning the Whin sill, three things are far from evident : 
1. The time of its origin. 2. The manner of its introduction among 
the limestone strata, 3. Its relation to the two great Whin dykes just 
described. On these subjects Professor Sedgwick and Mr. Wm. Hutton 
have delivered contrary opinions. My own investigations lead to the 
following deductions. 
The Whin sill is of date anterior to the east and west lead veins 
of Tynedale, Teesdale, and the Penine chain: for it is divided by 
these veins of fissure, exactly as the limestones are, and yields the 
same metallic riches in considerable proportion. At Troutbeck foot 
an intersection of veins yielded lead ore more abundantly in basalt than 
in any other stratum. It has been before shewn that these veins appear 
so related to the great axis of convulsion as to be a consequence of 
these disturbances. The Whin sill then is older than most of the 
saliferous system. It follows inevitably that the Cockfield dyke, 
which at its eastern end divides the oolitic strata, is not coeval with 
the Whin sill. But yet its direction and attendant phenomena, as 
well as those of the Quarrington dyke, indicate a centre of eruptive 
force in Teesdale, and we thus perceive reason to believe that more 
than one eruption of basaltic lava rose through openings in that valley 
at distant epochs of time. 
Was the basaltic lava poured out on the bed of the sea at one or 
several epochs during the deposition of the limestone series, so as to be 
quickly covered by these deposits, and thus be interstratified amongst 
them ; or did the eruptive lava during a later period force its way into 
the previously deposited rocks, along their surfaces of stratification, and 
thus elevate the whole mass of superjacent strata, as appears to have 
happened on a smaller scale in many situations ? Professor Sedgwick, 
in advancing the latter view, appears to have been much influenced by 
the local metamorphism of adjacent strata, by the partial unconformity 
between these and the Whin, and occasional inclusion of portions of 
their substance in its interior ; Mr. Hutton, on the contrary, has given 
more importance to the leading fact of its general conformity over a 
