“Why, putting off in a boat on salt water. We can’t do that without some fresh water on board. I’ve already begun the filling of the kegs by thimblefuls. It promises to be a slow process, as the spring seems unable to yield more than a gill or so at a time.”
“But, Cal,” interrupted Tom, “we can get all the water we want by digging a little anywhere around here. It doesn’t lie three feet below the surface.”
“Neither does the fever,” answered Cal.
“How do you mean?”
“Why, I mean that the milky-looking water you find by digging a few feet into the soil of these low-lying lands is poisonous. It is surface water, an exudation from the mass of decaying vegetable matter that constitutes the soil of the swamps. To drink it is to issue a pressing invitation to fever, dysentery and other dangerous and deadly diseases, to take up their permanent residence in our intestinal tracts.”
“But why isn’t the water of our spring just as bad?”
“Because it isn’t surface water at all, but spring water that comes from a source very different from that of the swamp soil. You have perhaps observed that the bottom of our spring is composed of clean, white sand, through which the water rises. That sand was brought up by that water from strata that lie far below the soil.”
“What makes it brackish, then?”
“It is brackish because a certain measure of sea water from the creek there sipes into it. The sea water is filtered through the sand, losing most of its salt in the process. You’ve noticed, perhaps, that the spring water is more brackish at high than at low tide. That’s because—”
“Oh, I see all that now. I hadn’t thought of it before. But really, Cal, it seems rather hard that we must sail away from here just when we’ve run up against something mysterious and interesting. Now, doesn’t it?”