What could have obliterated all signs of the interval during which the change from non-glacial to glacial conditions took place? The revolution in temperature may certainly have occurred during an intervening period when dry land existed. But as there are no traces of a land-surface, so far as I have seen, between the middle sand and upper-clay, I would suggest that the commencement of the upper-clay submergence may have been sudden, so as to generate an earthquake-wave capable of accomplishing the sweeping denudation of the sand which is so forcibly suggested by the clean and persistent line of separation above described.
Striated Rock-surfaces and their Relation to the Direction in which Erratic Stones have been carried.—I very lately saw a fresh exposure of intensely striated rock, from which a covering of upper Boulder-clay had been removed. It is a part of a more extensive display which has been demolished by quarrying operations, and occurs about a quarter of a mile south of St. James's Church, Birkenhead. The striæ, including large grooves, point to between 25° and 30° west of N. A short distance southward I found striæ pointing W. 30° S. As the extent to which the directions of the striæ vary in the neighbourhood of the estuaries of the Dee aud Mersey does not seem to be generally known, I would state that I have seen an extensive series near St. Silas's Church (north of Prince's Park, Liverpool) pointing N. 35° W., with a few cross striæ running between N. 38° W. and N. 40° W. In Toxteth Park, Liverpool, Mr. Morton, F.G.S., has found striæ pointing N. 42° W.; at Kirkdale, N. 15° W.; and at Oxton, Birkenhead, N. 30° W. I have reexamined grooves (including one more than three inches in breadth) close to the new Mission-house, Borough Road, Birkenhead, which were first noticed by Mr. Bostock, and found them pointing N. 45° W. If we connect these instances with that found on the east side of Hope Mountain, near Caergwrle, where I found the striæ pointing to about N. 45° W., we shall have striæ ranging from N. 15° W. to N. 45° W., which will include the main directions in which erratic stones (including Cumberland and Kirkcudbrightshire granite and Irish chalk-flints)[1] have travelled from their respective points of dispersion, though we have no reason to suppose that they travelled in straight lines. As Mr. De Ranee lately observed at a meeting of the Liverpool Geological Society, these striæ can be much better explained by floating ice than by land-ice; and it may be added that the floating ice may have been blown by wind as well as carried by currents, as proved by observations made by the late Austro-Hungarian Expedition in the neighbourhood of Franz Josef Land. It is well known that the directions of the striæ above noticed are crossed in the Isle of Man by striae from the E.N.E., and in Anglesey by striæ from between N. 25° E. and 30° E.,—that is, from the direction of the Lake-district. In Anglesey there are true roches moutonnées (Geol. Mag. for Jan. 1872), but there are no decided instances
- ↑ These flints are most numerous about Parkgate. They thin out S. and S.E. until they come into collision with flints from the eastern counties, which thin out westward.
