Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/901

 ' Edinburgh Philosophical Magazine,' with which I was unfortunately unacquainted when I wrote.

General Observations. — Two beds of Boulder-clay have been shown to occur over the whole of Western Lancashire, divided by a stratum of sand and gravel, often 60 feet thick, but sometimes thinning out so as to cause the two clays to coalesce. The thinning out appears to have been caused, as pointed out by Mr. Hull, by the denudation of the Middle Drift before the deposition of the Upper Boulder- clay, which thus unconformably overlaps the Middle and Lower Drifts. This denudation appears to have been partly marine, and partly possibly subaerial. Mr. Binney, however, still appears to consider the two clays to be one deposit, with an occasionally wedge-shaped mass of sand and gravel intercalated in its midst, absent in places merely because it was not universally deposited over the country. Thus, in his admirable description of the Blackpool cliffs of Glacial Drift, he gives the following classification : —

1. Brown clay, mixed with stones 4 to 5
 * ft. ft.

2. Brownish-coloured clay, used for " Till," containing much lime, often replaced by stratified beds of sand and gravel 80

3. Silt, lightish brown, with a few pebbles 2

4. Brownish-coloured Till, with stones to the extent of one-third of the mass exposed 30

In the section accompanying this paper (from Rossall to Blackpool), he represents two masses of sand and gravel disconnected from each other, the northern mass stopping abruptly near the top of the cliff under the Boulder-clay, and the southern mass near the " Royal Edward" (now Bailey's Hotel) also stopping abruptly in the midst of the Boulder-clay occurring all around it. I have now, from time to time, for more than a year, examined this section after heavy storms, and especially when the embankment was in great measure washed away in the spring of last year. I then became convinced that the thin bed of sand under Bailey's Hotel can be continuously traced behind the embankment under the Imperial Hotel until it connects itself with the great mass of sand, with occasional beds of gravel, which, commencing at the little brook called the Gynn, extends to Bispham. Between these two points the Middle Drift is about 60 feet thick, its base being, for the most part, but little above the base of the cliff ; but here and there the Lower Boulder-clay rises in the form of a boss or dome. The chief of these occurs near Bispham, where the clay is densely packed with stones, nearly all of which are scratched. The clay forms a low arch, the crown of which is about 22 feet above the base of the cliff ; it is separated from the overlying sand by a bed of silt or sandy clay, which is also arched, dipping under the beach at either end, and about 14 inches in thickness. It is the third bed of Mr. Binney's Table and Sections. He has also described an arch of silt covering a boss of Lower Boulder-clay under Bailey's Hotel ;.