XXT. 



OX THE nrroETANCE of recording erratic blocks. 



By H. George Pordham:, r.Gr.S. 



Read at Watford, Uth December, 1880. 



A Committee of the British Association has now been in existence 

 some years, for the purpose of "recording the position, height 

 above the sea, lithological characters, size, and origin of the Erratic 

 Blocks of England, Wales, and Ireland, reporting other matters 

 of interest connected with the same, and taking measures for their 

 preservation." As a member of this Committee, I am anxious to 

 bring before the Hertfordshire ^Natural History Society a brief note 

 on the work being carried on by the Committee, in the hope that I 

 may thus be able to obtain such assistance as may enable me to 

 compile a report, as complete as possible, on the erratic blocks, or 

 boulders, of the County of Hertford. 



The recording of scattei'ed boulders is a work which it is parti- 

 cularly desirable should be taken up by local scientific societies, 

 as it is only by the development of a wide-spread interest in the 

 matter that anything like a complete catalogue and description of 

 the erratic blocks scattered over the country can be hoped for. 

 Obviously the value of the ultimate deductions from, and of the 

 additions to, our knowledge of the Glacial period, depends, in a 

 great measure, on the completeness of the records obtained, and 

 their general extension over the whole of the area under con- 

 sideration. 



The title of the Committee to Avhich I have referred expresses 

 concisely its aims, but it will, perhaps, be useful if I a little further 

 explain what those aims are, and indicate more generally the raison 

 (Vetre of the Committee, and how we, in Hertfordshire, can best 

 contribute to the advancement of science in this particular matter. 



It must have come under the notice of the most casual observer, 

 that we have in various parts, and spread over large areas in 

 England, masses of gravel, sand, and clay, containing fragments 

 of a great number of dilferent rocks, otherwise unknown in the 

 districts in which these fragments now occur. These beds lie high 

 on the hills throughout Hertfordshire, and are found plentifully 

 distributed over all the midland and northern counties of England. 

 They are more ancient than our river-gravels and the sands and 

 clays which we find along all our water-courses ; for we find in 

 the river-deposits, fragments of rocks, and other traces of these 

 older beds. It does not, however, appear that, at the time when 

 the older clays and gravels were deposited on our hills, the face of 

 the country differed in any very material degree from its general 

 configiiration as we now see it. The valleys have been deepened 



