Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/848

736 736 D. MACKINTOSH ON SOME NEW SECTIONS 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 gene- rate 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 stria?, including large grooves, point to between 2b° and 30° west of N. A short distance southward I found striae pointing W. 30° S. As the extent to which the directions of the striae 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 1ST. 35° W., with a few cross striae running between K 38° W. and N. 40° W. In Toxteth Park, Liverpool, Mr. Morton, F.G.S., has found striae pointing N. 42° W. ; at Kirk- dale, N. 15° W. ; and at Oxton, Birkenhead, N. £0° W. I have re- examined grooves (including one more than three inches in breadth) close to the new Mission-house, Borough B,oad, 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 striae pointing to about N". 45° W., we shall have striae ranging from N. 15° W. to K. 45° W., which will include the main directions in which erratic stones (including Cumberland and Kirkcudbrightshire granite and Irish chalk-flints)* 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 striae 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 car- ried 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 striae above noticed are crossed in the Isle of Man by striae from the E.N.E., and in Anglesey by striae from between N. 25° E. and 30° E., — that is, from the direc- tion of the Lake-district. In Anglesey there are true roches mou- tonnees (Geol. Mag. for Jan. 1872), but there are no decided instances until they come into collision with flints from the eastern counties, which thin out westward.
 * These flints are most numerous about Parkgate. They thin out S. and S.E.