AND LOAMS OF WEST HEUTS. 1()3 



It is almost unneoossary to state tliat the qiiartzites, quartz, 

 felspar - porphyry, etc., have Leeii transported from a distance, 

 but it is difficult to decide from what localities. A section of 

 quartzite cut from a specimen taken from a Watford gravel-pit 

 appeared, when examined under the microscope, to be very similar 

 to specimens found in the Xew Ked Sandstone of the Midlands. 



Boulder-Clay. 



The clay at Bricket Wood is believed to have been produced 

 by the action of ice, most probably land-ice, which ground down 

 the subjacent rocks into a tine powder, or rock "flour," and left 

 this behind as a clayey deposit. 



The boulder- clay rests on a deposit of gravel and sand, similar 

 to those described above, and reaches a thickness of about 40 feet. 

 It contains flints, flint-pebbles, Jurassic and other fossils, chalk, 

 septai'ia, quartzites, and grits. Most of these materials are 

 believed to have been transported from distant deposits by the 

 moving ice. When fresh the boulder-clay is of a bluish colour, 

 but when weathered it becomes brown. It is very plastic, but 

 remarkably tough when fairly dry, so tough, in fact, as to be very 

 difficult and expensive to excavate. 



Gravelly Clay. 



In the extreme north-western part of the County, near Marston 

 Gate, there is a thin deposit of gravelly clay lying above the Gault. 

 About two-thirds of an average sample consisted of dark-coloured 

 clay, apparently derived from the denudation of the Gault, and 

 the remainder mainly of dark red, light red, brown, and grey 

 quartzites, fine-grained breccias, coarse grits, flints, and quartz- 

 pebbles. The quartzites, and some of the other rocks found in the 

 clay, are similar to some of those found in the gravels in the 

 southern part of the County. 



Chalk-Pebble Gravel. 



The last deposit which will be described is that which is shown 

 on the map near Long Marston as chalk-pebble gravel. It is thin, 

 and is remarkable for containing an exceedingly large number of 

 chalk-pebbles of all sizes, from that of a pin's head up to an inch 

 in diameter. These pebbles, which are often hard, form about 

 half the deposit, the other half being made up of unworn and 

 subangular flints, isolated masses of Greensand, and a little oxide of 

 manganese. The gravel is worked for road-metal, for which it is 

 suitable, after being coarse-sieved and then weathered. Section 10 

 shows the bed exposed south of Gubblecote. There can be little 

 doubt about the formation of these chalk -pebbles by the action of 

 water, and it is probable that they are the remnants of a shore- 

 deposit which was formed by a sea, or an arm of the sea, which 



