10 CORNISH POST-TERTIARY GEOLOGY. 



Crowan, and tlie sands and clays of St. Agnes, are the oldest deposits 

 on record, and might be even referred to the Tertiary period. 

 Between these and the Kaised Beaches, with which the unbroken 

 record commences, save in occasional Boulder-gravels at high levels, 

 we have no connecting links. The numerous excellent examples of 

 Raised Beaches and stony loam, or * Head,' Avhich Cornwall affords, 

 owing to the greater extent of its Palaeozoic coast-line, and the com- 

 pleteness of the stream-tin sections, not only make the Pleistocene 

 history of Cornwall more interesting than that of Devon, but to a 

 certain extent make up for the absence of cavern deposits. As it is 

 not possible to treat deposits of different ages, when associated in 

 the same sections, separately, I have noticed Head and Raised 

 Beaches together, and embraced under the head of stream-tin the 

 deposits overlying the submerged forests, reserving the last place 

 for a brief notice of Blown Sands and Gravel Bars. In the second 

 part of the paper I propose to weave these materials into chrono- 

 logical order. 



OLDEST DEPOSITS. 

 CroHsn Down Gravel. 

 Upon Crousa Down, in the Lizard District, a patch of quartz 

 gravel occurs at a height of about 360 feet above the sea, or about 

 20 feet lower than Roskruge Beacon. The ground is nearly level, 

 with a slight slope toward the south. It has been described by the 

 Rev. E. Budge.' I obtained the following section of the gravel pits, 

 which are from six to twelve feet in depth : 



1. Brown earthy soil, vrith angular stones and pebbles of qnartz, 



lying unevenly upon 1ft. to 4ft. 



2. Eeddish-brown earthy sand, with angular fragments of quartz \ 



3. Light-brown and grey clay, containing patches of tine quartz ) 6ft. 



gravel and loamy sand in places ) 



Below this the section was concealed by talus. The base of the 

 gravel is not shown ; the sides of two ponds at the bottom of tlie 

 pits are composed of quartz gravel. , 



On the opposite side of the pit to the foregoing, the deposit is 



represented by quartz gravel of irregular pebbles and subangular 



fragments, those of small size predominating, in brownish loam, 



exhibiting no signs of bedding. On some parts of Crousa Down 



1 Trans. Roy. Geol. Soc. Corn. vol. vi. pp. 1 and 91. 



