480 Correspondence — Mr. T. M. Reade. 



Silurian Graptolites ; and, finally, the fact that their equivalents are 

 everywhere separated from the equivalents of the Wenlock Eocks 

 by the main mass of the Middle Silurian, leaves us no choice but to 

 assign them to the Lower Llandovery. Ohakles Lapworth. 



St. Andrews, Sept. Wi. 



SECTION" OF BOULDER-CLAY, NOETH DOCKS, LIVERPOOL. 



Sir, — The sections described by Mr. Mackintosh in the September 

 Number of the Geological Magazine are, as he says, well worthy 

 of study. They were visited by the Liverpool Geological Society in 

 June last : at that time the section showing the Lower Boulder-clay 

 of Mr. Mackintosh was wrell developed. It was simply a clay con- 

 taining more stones and of a harder nature than usual, separated 

 from the clay above, which is more plastic and free from stones than 

 is generally the case, by a seam of sand and gravel. Several of our 

 members were rejoiced at having at last discovered that for which 

 they had previously for years searched the neighbourhood in vain, 

 viz. the veritable Lower Boulder-clay. I ventured to doubt if the 

 section before us was sufficient evidence to support the tripartite 

 division of the Boulder-clay now in fashion ; and I expressed the 

 opinion that the distinction would not be maintained over any 

 considerable area, and that the lower clay was simply a local varia- 

 tion of the upper ; in fact, that the deposit was one and the same. 

 A short time since I again visited the Docks, this time in company 

 with Mr. Bristow, Mr. Aveline, and Mr. De Ranee. The latter 

 gentleman, who is well acquainted with the excavations, was desirous 

 of showing us a section of some curiously contorted gravels, and 

 took us to the exact site of the previous Lower Boulder-clay section, 

 but — though certainly not to my astonishment — both contorted 

 gravels and Lower Boulder-clay had disappeared. The fact is, the 

 beds are thrown about so irregularly that there is no dependence to 

 be placed on their continuity. A few yards more or less of excavation 

 changes their character so, that what before appeared separate and 

 distinct beds shade into one another by imperceptible gradations, 

 thin out, or, as not uncommonly happens with beds of sand or 

 gravel, stop short off with a square end. My friend Mr. De Ranee, 

 if my memory serves me, also expressed the opinion that there was 

 no Lower Boulder-clay in the dock. So far as the Boulder-clay 

 deposits about here affect the question, I have arrived at the mature 

 conviction, after long study, that between the red sand or rock on 

 which they rest and the surface they are an unbroken series of 

 marine deposits, laid down during the subsidence of the land and 

 its subsequent re-elevation, and that for an explanation of the curious 

 manner in which they are bedded we must look to the varying 

 directions of the tidal currents as affected by the degree of sub- 

 mergence at the time, and the contours of the then land. 



4, South John Street, Liverpool, Sept. I2th. T. Mellard Reade. 



ERRATUM.— In Mr. Bonnet's letter, p. 377, lines 30, 31, from top of page, for 

 " therefore it is to be applied," read " it is not therefore to be applied." 



Dr. Oldham begs us to delete, at p. 384, the letters C.B. after his name. "We 

 apologize for the error. Edit. Geol. Mag. 



