THE SEVEllN TUNNEL SECTION. 93 



ofeervosced slightly with acid. The bed of Shalo containing 



1 ■ ■ ■ ■ O 



lumps ot Mountain Limestone is puzzling. From the de- 

 scription Mr. Jones gives, I should be disposed to believe 

 that the limestone was originally interstraiijied with the shale. 

 The section shows how much the bods are broken and dis- 

 arranged near this point. One would be glad to know 

 whether any fossils were found in this limestone. Mr. 

 llichardson does not i-emomber having seen any. llenieni- 

 boring that Port-Major Austin described beds of Limestone 

 as occurring in the Millstone Grit, one cannot but feel some 

 doubt as to whether the true Mountain Limestone, or even 

 the Upper Limestone Shales, were reached. The Millstone 

 Grit in the Forest of Dean is nearly 500 feet thick. Near 

 Bristol it is nearly twice that thickness. The thinning out 

 of the Lower Coal Measures is remarkable. Here again, one 

 cannot but regret that the broken character of some of the 

 beds should make one fool that any interpretation of the 

 sequence here may possibly bo somewhat " at fault." 



4. The liiver Channel. — There can be little or no doubt 

 that Mr. Charles Richardson is correct in ascribing the 

 ' Shoots " channel to tlie wear and tear of the river bed, 

 duo to special denudation along this lino. Mr. Stoddart's 

 " ancient fissure " theory is practically out of court. There 

 is one remark in Mr. Richardson's paper, however, to which 

 I should like to draw attention. He says, " The Shoots 

 Channel, as you ascend the river, points towards the Welsh 

 shore, so that the in-flowing tide presses against the Welsh 

 shore ; while, on tho other hand, the main stream of the 

 ihbing tide is flung towards tho English shore by tho pro- 

 .iecting point of St. Tocla's Chapel Rock, thus leaving an 

 intermediate sandbank, called the Dun Sand, in the middle 

 of tho river, between the up and down currents. The ebbing 

 tide, thus thrown on to the English side, passes over the 



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