There are places in Godfrey’s Glen where half the scoria layer is made up of crystal-rich bombs up to 2 feet in diameter, and for each old lava fragment more than an inch across there are at least fifty of these large bombs of scoria. At such places, the total percentage of lithic fragments by volume is not more than 5. Pieces of old lava more than a foot in maximum dimension are exceedingly rare. In the finer matrix of the scoria, the proportion of lithic detritus may be considerably higher, as the diagram, figure 26, shows.
At the head of the glen, near Dewey Falls, the scoria layer descends to the valley floor, the pumice flow being absent. Farther downstream, the pumice appears beneath the scoria and both continue to thicken. Nowhere is there a clean-cut contact between the two types of flow, yet the transition zone in all places is quite thin, ranging generally between 10 and 20 feet. This sudden change in the character of the deposits, from dacite to basic scoria, deserves to be borne in mind.
In the pale pumice layer there are short and irregular brown streaks, running almost horizontally. These may signify brief periods of fumarolic activity between successive flows. There are also small lenses of reworked glacial debris within the pumice. It does not follow, however, that these were laid down during long intervals of erosion; they are more likely to have been caused by floods accompanying the pumice flows as they melted snow and ice in their path.
In many short stretches, Annie Creek has already cut through the pumice and scoria deposits to the underlying glacial moraines and bedrock lavas. Wherever the contact is exposed, it is emphasized by copious springs, the seepage line clearly defining the hummocky surface of the recessional moraines. Occasionally small pieces of carbonized wood may be collected close to the base of the pumice in Godfrey’s Glen, proof that at least a few trees were growing this far up the valley before the eruptions began.
