210 Capt. Huttoris Geological Report. [No. 111. 



As, however, trap is known to possess, " in a general sense, the univer- 

 sal common character of being unstratified, and posterior to the rocks 

 with which it is connected,"* it becomes necessary in here stating, that 

 it is conformable to and interstratified with those of the secondary series, 

 to offer a few theoretical remarks on the probable means by which this 

 partial stratification has been produced. 



The interstratification of this rock, where it occurs, is of very inconsider- 

 able extent, when compared with that of those with which it is associa- 

 ted, possessing by no means the wide and almost universal range of the 

 primary and secondary series, but being on the contrary, " in a great 

 measure limited to particular spots, more or less extensive, and to be, if 

 separately considered, partial and independent productions. "f 



Let us then suppose that these secondary strata were once (which in fact 

 they really were) horizontal deposits from the waters, which it is generally 

 supposed were instrumental to the formation of the series to which they 

 belong. 



We shall thus perceive them to have been deep unconsolidated masses of 

 sands, covered by muddy layers, which we now term shales. The strug- 

 gles of the molten matter to procure access to the surface would, from the 

 heat and pressure engendered by its upward course, have the effect of 

 vitrifying and indurating the sands through which it forced a passage, 

 and of converting them into strata of sandstone, while the shale or 

 muddy deposit next in succession being lighter and less massive than 

 the stream of trap, would probably rise and yield a passage between 

 itself and the sandstone for the molten matter to form a stratum, some- 

 what in the same manner as oil would give place to a stream of water 

 if injected through a tube or aperture below it. 



The muddy deposit, however, being hardened by contact with the lava 

 and by the general pressure of the uprising strata, would burst as the 

 sandstone had already done, and yield a passage to the trap, which 

 flowed through and overspread them at the surface. 



Should it be contended that the outburst of a stream of lava such as 

 that I have described the trap to have been, would have expended 

 itself in a shower of ashes or cinders, rather than have assumed the 

 stratiform structure it now exhibits, I would remind the reader that 

 the secondary rocks are supposed to have been deposited in the bosom 

 of a tranquil water, and that that water formed either extensive lakes or 

 portions of the sea. 



t McCulIoch's Geology 



