and Phcenomena of the Couny of Suffolk. 365 



Diluvium*. — The diluvium of Suffolk may be divided into three classes : 

 1. clay; 2. gravel; 3. erratic blocks. 



1. Diluvial clay. — This deposition covers a great portion of the county, and 

 extends into Norfolk, Cambridgeshire and Essex, rising to a considerable ele- 

 vation in High Suffolk, and having, near Cromer, a thickness of 400 feet. A 

 large portion of the clay is of a yellowish hue, but the greater part is blue ; 

 and both varieties contain chalk pebbles, sometimes disposed in layers, but 

 more commonly dispersed, a character by which the diluvial clay may be di- 

 stinguished from the London or plastic clays. It is difficult to determine the 

 origin of this argillaceous deposit ; but I am inclined to think that the yellow- 

 ish portion may have been derived from the plastic clay, and the blue, in con- 

 sequence of its peculiar fossils, from the clays below the chalk. Fragments of 

 coal have been found in the diluvium at Lavenham, also fragments of mica 

 slate containing garnets and tourmaline. Specimens of a similar rock were 

 found by Mr. R. C. Taylor at Cromer, with masses of granite, porphyry, trap, 

 oolites, and every other rock above the coal-measures. At Ballingdon Hill, 

 near Sudbury, Mr. Brown has procured thirty varieties of primary, secondary 

 and tertiary rocks. Comparatively few flints occur in the clay. At Ickworth, 

 a beautiful specimen of the Dudley trilobite was obtained in making a drain, 

 and at various other localities, numerous tertiary and secondary fossils abound. 

 It is inferred that the clay contains cavities, as streams of foul air occasionally 

 issue from fissures. 



It is difficult to define accurately the boundary of the clay. Smith's map is 

 correct in the general outline. The eastern limits range from Wangford near 

 Southwold, with occasionally slight interruptions,, to Parham, Otiey, and 

 Henley. Passing the Gipping, it extends to Shelley, and thence to Clare, 

 Haverhill, and Newmarket. Prom the last locality it may be defined by a line 

 passing from the edge of the chalk to the N.VV. into Norfolk. 



2. Gravel. — The gravel is less generally diffused than the clay, and though 

 there are instances in which it underlies the clay, and others in which the 

 two are mixed up, yet I consider the gravel to have been partly deposited 

 at a distinct period. In some places, as near Sudbury, it consists merely of 

 unrolled flints ; in others, large masses of flint, slightly mixed with chalk peb- 

 bles, are imbedded in sand ; and occasionally, flints are intermingled with 

 bowlders, of various dimensions and sometimes unknown origin. Many of the 

 extraneous fragments found in the gravel, I think may have been washed out 

 of the clay ; and I am of opinion that the river valleys have been excavated 

 both through the clay and the gravel. With regard to the relative propor- 



* For references to detailed sections see the numerical index, p. 368. 

 3b2 



