582 TRIMEVAL MAN, 



preme, and every investigation of the superficial deposits was 

 tinged, more or less, of a glacial complexion. The gravels, 

 sands, and loams, not directly the products of glacial action, 

 were in every respect unattractive. True that they were 

 occasionally loaded with organic remains, the most important 

 of these being fossil bones ; but the latter were regarded in 

 most instances as being but repetitions of what was already 

 well known; the deposits themselves were of local 'origin, 

 and in many cases their precise geological age long baffled 

 all attempts at determination. One signal example to which 

 frequent reference will be made in the sequel may be ad- 

 duced. In the Valley of the Thames, close to the head- 

 quarters of geological observations in England, there is 

 an abundant development of loam and gravel deposits of 

 freshwater origin, which are extensively excavated for brick- 

 earth and other commercial objects. They contain beds 

 which are charged with fluviatile shells, some being of 

 species now extinct in England ; and they are also rich in 

 fossil bones of large Mammalia, living and extinct. Fine 

 sections of these beds have been disclosed at Brentford, 

 Ilford, Grays Thurrock, Erith, and other localities. The 

 Brentford section was described fifty years ago in the ' Philo- 

 sophical Transactions,' and some of the most remarkable 

 organic remains found in it were at the same time figured. 1 

 The Grays Thurrock beds were closely studied by an able 

 and experienced observer, Professor Morris, who published 

 an excellent account of their contents in 1838. The whole 

 series of these brick-earths, both in the Valley of the Thames 

 and in other river valleys of the same system, has been the 

 subject since of constant observation by some one of numerous 

 geologists of authority, such as Godwin- Austen, Prestwich, 

 Morris, Joshua Trimmer, Lyell, Edward Forbes, &c, yet 

 has their true geological age, whether preglacial, i.e. an- 

 terior to the submergence of the land under the glacial sea, 

 or post-glacial, i.e. subsequent to its final emergence, re- 

 mained up to the present time a subject of the utmost per- 

 plexity and of great difference of opinion among geologists, 

 the reason of this being that nowhere in the Valley of the 

 Thames was a section to be found showing the glacial drift 

 and fluviatile deposits in contact or in order of superposition. 

 The general physical phenomena, in the absence of direct 

 proof, led Mr. Prestwich, Professor Morris, and the late Mr. 

 Joshua Trimmer, to the belief that they were of a later date 

 than the Boulder-clay, i.e. post-glacial, while the palseonto- 

 logical evidence appeared to be at issue with that inference, 

 and to indicate that they were preglacial. The polyonomous 



1 William Trimmer, Phil. Trans. 1813. 



