Pebble abundance changes between each unit (Fig. F2). Unit 1 has the fewest pebbles (46) and fewest samples with >1 pebble (seen as peaks in Fig. F2). Unit 2, with the most pebbles (209), also has more peaks than any other unit. Unit 3 has fewer peaks than Units 1 and 2 but contains the largest peak (29 pebbles) of any unit.
Slight changes in lithology over time are present in the pebbles sampled for this study, which could indicate a change in sediment provenance. The percentage of metamorphic lithologies decreases with time from 62% to 41%, whereas intrusive lithologies increase from 8% to 20% (Fig. F3). There is a sharp increase (5% to 66%) in the number of mafic volcanic pebbles between Units 3 and 2, although there is no significant increase overall in volcanic clasts. The proportion of sedimentary lithologies remains consistently low throughout.
The relative abundance of each of the different clast shapes is constant through time, except for an increase in the proportion of rods from 9% to 19% (Fig. F4). Discs are the most common shape in all units, spheres are the next most common, but the proportions of blades and rods vary. Shapes of the pebbles appear to be controlled to some degree by their lithology. Discs are the most common shape for all lithologies, except intrusive igneous rocks (Fig. F5), for which spherical shapes are the most common. Rods are slightly more common than blades in volcanic and intrusive pebbles, whereas for metamorphic and especially sedimentary pebbles, blades are more common than rods.
Values of visual roundness are between 0.1 and 0.6 for Units 2 and 3 (Fig. F6). For Unit 1 the majority of pebbles have values of roundness between 0.3 and 0.5, with slightly fewer at 0.3 and no pebbles of value 0.1. Unit 1 has a higher percentage of pebbles with values of roundness of 0.3 than any other unit. In Unit 2, visual roundness values increase steadily from 0.1 to 0.5, then drop off sharply at 0.6. Unit 3 contains equal numbers of pebbles of values 0.4 and 0.5 and a significantly lower percentage of pebbles of value 0.3 than other units.
In all units, most pebbles fall within the field of basal debris on the sphericity vs. roundness diagram, as defined by Boulton (1978). In Unit 1, one pebble plots within the field for supraglacial debris. All others may be interpreted as basal debris (Fig. F7). All three fields, supraglacial, basal, and lodgement, are clearly represented in pebbles in both Units 2 and 3, although pebbles plotting in the supraglacial and lodgement fields are not as common in Unit 3 as in Unit 2.