34 
H. G. FORD HAM—ON BOULDERS 
scale the distribution of the various rocks and classes of rocks which 
occur as boulders over the whole country. On such a map of 
boulders can be laid down, with more or less probability, the 
localities from which the various rocks have been derived and the 
courses the boulders have travelled from these localities to the 
places in which they are now found, and the general distribution 
of ice-borne rocks would then be seen at a glance. 
As a part of the most southern area over which this general 
distribution of boulders extends in England, Hertfordshire has 
some special interest, and although our erratics are not of such 
striking dimensions, or perhaps of such interesting materials as 
are some of those found farther north, they yet help to tell a story 
of much importance, and a knowledge of their characteristics will 
contribute towards clearing up the history of a period which, 
although very remote in point of time, has a distinct and tangible 
connection with the history of man, and the study of the present 
climatic condition of the earth. 
To note and record all the boulders now existing on the surface 
in Hertfordshire would involve a survey of the whole county. 
This can hardly be attempted by any one person ; but if some one 
could be found in each parish in the county who would for that 
parish note the boulders within its boundaries, the work would soon 
be done. It is convenient that it should be done with relation 
to small areas, such as that of a parish. Negative as well as posi¬ 
tive information is valuable. To know that boulders are absent 
from any parish or district so far removes our ignorance. Partly 
in order to show what may be done, and partly with a view of 
recording within the county what has already in the main been 
incorporated in the Reports of the Erratic Block Committee of the 
British Association, I now bring before the Society notes on the 
boulder-clays and boulders of the Parish of Ashwell, and of several 
other parishes and places in the north of Hertfordshire. 
The area I shall refer to lies in that district of the county 
bordering on Cambridgeshire and Bedfordshire which is north of 
the main ridge of the Chalk outcrop. Some short description of 
the superficial characteristics of the district, and of the position 
and character of the beds from which the boulders are derived, and 
their relation to the superficial geology and physical geography, 
are necessary in order that the present position of the boulder-clays 
and gravels and their connection with the changes which have 
taken place in the local configuration of the surface may be 'clear. 
In the map showing the river-basins of Hertfordshire in Yol. I, 
part 3, of our ‘ Transactions ’ (facing p. 127), a line running through 
Therfield and Stevenage, nearly S.W. and N.E., marks the water- 
parting between the streams draining into the Thames and those 
draining into the Ouse, and at the same time divides the country 
on the south, which is pretty-generally covered with boulder- 
clay or gravel, from the band of bare chalk, diversified with occa¬ 
sional patches of boulder-clay, with which I am specially concerned 
in this paper. 
