54 James Geikie — On the Age of the Crofthead Deposits. 



Boulder-clay of the locality m question contains certain intercalated 

 beds of clay, sand, and gravel which have yielded Bos primigenius. 

 Quite recently the remains of the horse and the great Irish deer 

 have been met with in the same deposits. In the present paper I 

 do not mean to say more about the character of the stony clay 

 which overlies the beds with mammalian remains. There can be no 

 doubt whatever that it is truly Boulder-clay. But as I understand 

 that several members of the Glasgow Geological Society have since 

 visited the section, and, while agreeing with me as to the glacial 

 origin of the overlying Till, have yet expressed an opinion that this 

 bed is not in its natural position, but has slipped down upon the 

 stratified deposits from the adjacent hill-slope, it may be well to 

 point out how all the facts are against such a supposition. 



1. The bedded deposits of clay, sand, and gravel do not differ in 

 the slightest degree from similar intercalated beds of very common 

 oeourrence in the Lower Boulder-clay of the south-west of Scotland. 

 Along the numerous stream-courses of West Lanarkshire, Ayrshire, 

 and the neighbouring counties, abundant evidence on this head will 

 convince the most sceptical. I may add that near to the bottom of 

 the i?os-beds I obtained from finely laminated clay a few scattered 

 stones, all well striated — the smallest not bigger than a walnut, the 

 largest about the size of one's fist. Here again we have a repetition 

 of phenomena common to the Boulder-clay of the west and east of 

 Scotland. In the valley of the Tweed, for instance, we have alter- 

 nations of tough yellow Boulder-clay with beds of gravel (often full 

 of scratched stones), and considerable thicknesses of sand and 

 laminated clay, which occasionally exhibit a few scattered erratic 

 blocks and striated stones. The same appearances are repeated in 

 the valleys of the Stinchar, the Ayr, the Doon, the Irvine, the Avon, 

 the Clyde, and their numerous tributaries. There can be no doubt 

 that these bedded deposits are truly intercalated with the Boulder- 

 clay, for excellent sections, which the merest tyro will understand 

 at a glance, frequently present themselves in flat undulating country 

 where there cannot be any possibility of intermittent landslips 

 having occurred. 



2. Throughout the trappean district in the neighbourhood of 

 Crofthead, and for many miles to the west, south, and east, the hill- 

 tops and steeper hill-slopes are singularly bare of Boulder-clay, that 

 deposit being only met with in the bottoms of valleys and sheltered 

 hollows, and here and there sparsely scattered over the gentler hill- 

 slopes. 



3. The overlying Boulder-clay in the Crofthead section is only a 

 continuation of the same deposit which, increasing in breadth as the 

 valley widens to the south-west, creeps further up the gentler 

 valley-slopes in that direction than it does where the valley con- 

 tracts and the hill-slopes become steeper. Hence the position of the 

 Boulder-clay in this valley is quite natural, and just what one would 

 expect to find. 



4. The underlying laminated clays, etc., are in places highly 

 crumpled and contorted, and the foldings are so arranged as to show 



