S. V. Wood, Jun. — Sequence of the Glacial Beds. 61 



wero in question ; but admitting, as I do with Mr. Scropo, tliat tlie 

 rocks involved in those processes all, so lar as wo know, contain 

 water, there probably intervenes, as I have elsewhere endeavoured 

 to show, a diflerent law. As explained in a paper on the probable 

 seat of volcanic action (Geol. Mag., June, 18G9), I regard the 

 liquidity of the stratum in which I place the seat of volcanic agency 

 as due, not to simple igneous fusion, but rather to an igneo-aqueous 

 fusion, as maintained by Scrope, Scheerer, and Elie de' Beaumont, 

 where water at a high temperature, aided by pressure, produces a 

 quasi solution. As I have there endeavoured to show, pressure, which 

 in the first case, that of simple fusion of anhydrous materials, prevents 

 liquefaction by preventing expansion, in the second case, on the 

 contrary, favours liquefaction by promoting solution of the water- 

 impregnated mass. As Sorby has shown, a conversion of mechanical 

 into chemical force appears in the increase of solubility under 

 pressure. In other words, pressiire prevents fusion when, as in 

 most instances, it is a process of expansion, but favors solution, which 

 is, with few exceptions, a process of contraction. Now since I place 

 the seat of volcanic action in a region where solution, rather than 

 simple fusion, is the cause of liquidity, I am led to regard pressure 

 as one of the efficient causes of the liquefaction of rocks, and to re- 

 gard its diminution as leading to solidification. This conclusion, 

 though in contradiction to the letter of Mr. Scrope's teaching, will 

 not, I venture to hope, be rejected by the master who first taught us 

 the true cause and nature of the liquidity of lavas. 

 Montreal, December 7, 1869. 



V. — Observations on the Sequence op the GtLACial Beds. 



By S. V. Wood, Jun., F.G.S. 



PAET II. 



(Concluded from the January Number, page 22.) 



Turning now to the physical evidence, it is well known that the 

 Moel Tryfaen bed is 1390 feet above the sea-level ; and a depression 

 which would bring the sea up to that point would, unless we suppose 

 a great change in the relative elevations, place the Chalk many 

 hundreds of feet beneath the sea. 



The Middle Glacial beds, which are chiefly composed of chalk flints 

 in the East of England, are also largely charged with the same 

 material, as far as I have traced them into the Oolitic, the Liassic, 

 and even the Triassic districts ; and they never, so far as I have 

 traced them, rise to elevations exceeding 420 feet, which is near 

 Eugby. In East Anglia they usually cease between 200 and 250 feet, 

 the bed e" overlapping them, and extending up the higher elevations ; 

 bnt in one instance (Danbury) they seem to go to the height of 

 360 feet. They occur at all less elevations, down to and below the 

 present sea-level. It is difficult to imagine, in the face of this, that 

 all the Chalk could have been below the sea-level during the forma- 

 tion of the Middle Glacial ; at any rate, it could hardly have been 



