320 ANNUAL REPOET SMITHSONIAN INSTITUTION, 1917. 



plane of marine denudation rising inland from 50 feet to about 90 

 feet and covered by blown sand of the later period. The seaward 

 margin of this plane is formed by a cliff against which the deposits 

 of the 25-foot submergence rest. To this submergence also Keade 

 attributes the " washed drift sand " imderlying the lower peat and 

 forest bed and containing remains of hazel. This 50-foot submer- 

 gence may also be represented by the higher terraces in some of the 

 Lancashire valleys. The evidence for its existence is not entirely 

 satisfactory, and the question would probably repay detailed study. 

 After this the succession is well marked, being — 



1. Lower peat and forest bed. 



2. Formby and Leasowe marine beds and Shirdley Hill sand. 



3. Lower Cyclas clay. 



4. Upper peat and forest bed. 



5. Upper Scrobicularia and Cyclas clays. 



These do not call for much remark. The lower peat and forest 

 bed begins with a layer of tree stools, resting generally on bowlder 

 clay, in the valleys which intersect the 50-foot plane of denudation. 

 They are overlain by peat up to a thickness of 4 feet. The character- 

 istic tree is hazel ; Ursus spelaeus has been found in the peat. 



The Formby and Leasowe marine beds and associated marine 

 deposits form the lower plain of Cheshire and Lancashire. Their 

 upper limit follows the 25-foot contour with great exactness. The 

 fauna gives no evidence of a climate differing from the present. 

 The Shirdley Hill sand consists of two facies, a marine facies at 

 lower levels, with Cardiwin edvle equivalent to the Formby and 

 Leasowe beds, and an seolian facies forming old sand dunes and ex- 

 tending over the upper plane of denudation. The marine beds gradu- 

 ually pass up into the fresh-water Cyclas clays. 



The upper forest bed rests on these marine and fresh-water beds, 

 and extends to a depth of 40 feet below sea level, indicating an 

 emergence to at least 50 feet above the present level. The trees in- 

 clude oak, pine, hazel, and birch ; some of the oak stools have a diam- 

 eter of as much as 7 feet, so that the climate was far more favorable 

 than now for their growth. The overlying peat reaches a thickness 

 of 12 feet. Its formation appears to have been completed before 

 Roman times. 



Passing inland, we find the slopes of the Pennines everywhere 

 peat covered and at present almost devoid of trees. In the peat, 

 however, is a well-marked forest layer, consisting of oak stools to 

 about 1,200 feet, hazel to 1,700 feet, and birch as high as 2,500 feet 

 (94) . As a rule at higher levels, the lowest vegetation, resting on the 

 bowlder clay, is of arctic type; this is covered by Phragtnites cam- 

 munis peat, on which the birch forest grew, and was afterwards re- 

 placed by moorland peat. At lower levels the forest bed usually 



