this was many days back , of course , and since then we had come to know other aspects of the great creature , and across the bavarian wheat plain of straubing she wandered so slowly under the blazing june sun that we could well imagine only the surface inches were water , while below there moved , concealed as by a silken mantle , a whole army of undines , passing silently and unseen down to the sea , and very leisurely too , lest they be discovered .