12G 



taken place in organic life during the epochs represented by these two forma- 

 tions, and, therefore, this range of hills is a testimony that the most powerful 

 dislocations may proceed concurrently with tho ordinary course of nature ; and 

 such is, perhaps, the most important lesson to be drawn from Sir C. Lyell's 

 volumes. The arguments he has accumulated from so many sources appear 

 completely to dispose of the notion that the upheaval of such a mass of rock 

 as we are now standing upon was a sudden event, or necessarily attended with 

 violent disturbance of the ordinary conditions of nature. This very moment 

 probably some infinitesimal movement is taking place in the rocks beneath 

 our feet, which, giving time enough for it to act, would be obviously capable 

 of producing any amount of change. "When we look at the upturned edges, 

 indeed, of these strata, when we find that at the very least computation they are 

 some ten or twelve thousand feet thick, we are disposed to think that some 

 mighty cataclysm must have thus dislocated them ; but it is the function of 

 true science to correct these random guesses, and to put aside any prejudices 

 derived from previous notions by a calm examination of facts. Such a prejudice 

 clearly exists in many minds. It is remarkable how many attempts have been 

 made to establish the paroxysmal theory ; yet can anything be more unscien- 

 tific than to assign causes other than we have experience of, unless an absolute 

 necessity compels us to do so. 



With respect to the structure of the mass of the Longmynd hills : they 

 consist of an accumulation of greenish-gray shales alternating in many parts with 

 purple beds of the same lithological character, and with occasionally more sandy 

 and quartzose rock. Their usual dip, when not disturbed by fault, is a high 

 angle of some 70 or 80 degrees towards the N.E., and thus, in traversing the 

 gorge from Church Stretton to the west, excellent sections are displayed, show- 

 ing their enormous thickness. Whether any doubling over of the strata occurs 

 in the flat table land of the summit is a question which has not been satisfac- 

 torily settled, but some good geologists think it probable, and so have reduced 

 Ramsay's estimate of 26,000 feet to probably 12,000 — a thickness quite suffi- 

 cient, however, to fill us with wonder if we think of how long it must have 

 taken to form. Imagine, e.g., how long it would take to fill up the bed of the 

 Atlantic to a depth of 2A miles at the present rate of deposit. 



These hills have, as has already been said, been the centre of several 

 o dilations of the earth's crust. They were possibly above water when the 

 Lingula flags were elsewhere being formed ; they then sank into the depths of 

 the ocean, to receive upon them the great mass of the Llandeilo rocks, which 

 count, I believe, some 3,000 feet in this neighbourhood (it was perhaps at the 

 commencement of this subsidence that the bed of conglomerate on their western 

 flank was accumulated) ; then, while elsewhere the Caradoc was forming, they 

 were xipheaved into their present nearly vertical position. Then again came a 

 period of subsidence, when the Llandovery conglomerate was formed along 

 their southern and eastern flanks. What was their position during the sub 



