Page:Popular Science Monthly Volume 74.djvu/513

Rh reader, it will be necessary to describe briefly the geography of the region.

No geologist has described the rock formation of Casco Bay, although many of the more salient points in its history are evident. A glance at the accompanying map will show that the bay is dotted here and there with islands, none of which are more than three miles in length. It is popularly said by the denizens of the region that there are as many islands in the bay as there are days in the year. However that may be, it seems to the traveler who is making his first visit by the little steamer threading through the devious passages between the islands, that the estimate has been too meager. Extending down from the mainland are several long ragged points of land. Harpswell is one, Cape Small Point is another. The axes of these peninsulas lie parallel with those of the islands and between the islands and the peninsulas are deep lagoons bordered by the steep high sides of the islands. The average depth of these lagoons is fourteen fathoms, although a greater depth is reached in some places. At the westward. Cape Elizabeth forms the boundary for the bay.

A portion of the Arctic current flowing down the Gulf of Maine from the Greenland and Labrador shores is deflected into the immediate vicinity of Casco Bay, giving the cool water and the cool air characteristic of the locality. The Gulf Stream lies beyond this cold current and, while rarely a bit of the fauna of this stream comes into the bay, its effect is practically nothing on the plant and animal life. The dense fogs so characteristic of some of our other laboratories, nearer the Gulf Stream, are nearly absent here. It is mainly for this reason that one may safely use apparatus at the laboratory without injury from rust and hydroxide and oxide depositions. The writer, during the past season, used apparatus of great delicacy, such as is seldom brought out of the city workrooms, in investigating the contractions of muscle in various invertebrates, without any deleterious effect being produced by its sojourn at the coast.

The geological structure of the region is such that the retreating tides leave tide-pools filled with a wealth of animals and plants. The range of the tides is great, averaging fourteen feet. The cleavage planes of the mica schist and slate are normal to each other so that square or rectagonal holes are left for the formation of the tide-pools. Here may be found Asterias, Strongylocentrotus, Metridium, Tetrastemma, Carcinus, Cancer and dozens of other species. The algalogist is well rewarded for any labor he may expend in working these pools. The lagoons were gouged out in preglacial times and therefore the rocks are bare and free from till and boulders to a great extent. The subsidence of the whole region in later times has deepened the water throughout the bay, and these deep lagoons are carpeted with immense