[92]

15

(King George Sound)

is worthy of attention

// especially in those dikes which are narrow

The fact of a system of dikes close together and running parallel to each other & close together, I recollect several instances of it in erratic countries, (-as an Quiriquina Island near Concepcion, two localities in the Chonos Archipelago, Bahia on the coast of Brazil, and in mica slate on the Eastern flank of the Cordillera of central Chile) where the number of dikes was not so great that their occurrence in a system  can possibly be thought [insertion:] attributed to be accidental is worthy of attention. In these instances, as at King Georges' Sound, are we to suppose, that the fissures, & [3 words illeg] the case of K G Sound, each two or three feet will and occurring with the space of a hundred yards, were formed at the same time & by the same force. Mr Hopkins* has shown that the [furiniation] of parallel fissures will probably result from a tension acting at the same time over a considerable area, since time is required to transmit the force from distant point transmission from distant points, but  will this [illeg] hold good in a width so excessively narrow compared with the thickness of strata probably fissured, as in the cases now under discussion? I am inclined to believe that in dikes (as well as in the axis of mountain chains, as I endeavoured to show in a paper read before the Geological Society) the several lines are generally of successive origin; the consolidation of the fluid matter in the first fissure being the [illeg] cause of the formation of the second; the tension sea action & under the same area. This also receives support grain the circumstances that the parallel dikes though close together are not unfrequently of slightly different composition (I observed instances of this at Concepcion and in the Chonos Archipelago). We could never expect to find such an occurrence if they had been formed at the same moment, although on the other hand, if formed successively they would often be of the same nature, & the same causes then these

[Im margin:] [Quote] [illeg] a country

[in margin:] good Keep this with S. America scraps

 

16

volcano ejects the same kind of lava at many successive eruptions, although at other times they might be injected with