In Skowhegan and Vassalboro', marine fossils have been found in the digging of wells, both cases being above 150 feet above tide water. In Clinton, there is another locality of marine alluvial fossils 40 or 50 feet above the Kennebec River.

The lower clays of this group at Bangor are very tenacious and adhesive, with the peculiar marine odor of marsh mud, and contain as characteristic shells the Nucula, Saxicava distorta and Mya arenaria. The upper portions of the deposit are more sandy. The clayey strata are of a yellowish cast, containing numerous yellow, soft concretions of clay of a cylindrical shape, and perforated by a long tube. Ferruginous and siliceous sands alternate with the clays. The lower portions of the upper beds contain Leda Portlandica, Mactra and Venus. The upper portions are filled with the concretions. Some of these clays in Bangor dip 10 degrees south-west, and others 15 degrees southerly. The highest of them is about 100 feet above the ocean. Above the clays are found coarse drift deposits.

In the south part of Cherryfield, there are numerous concretions in the clay, containing various fossils for their nuclei. Among others from this locality there have been found fossil fishes and fossil nereids, and an annelid or sea worm. A prolific locality of fossils is at the Plaster Mills, in Lubec. A large canal was dug there in which were found vast numbers of Pecten Islandicus, Saxicava distorta, Mya arenaria, Mytilus edulis, Modiolaria nigra and Balani. Marks of the fossils are found 36 feet above the bottom of the canal. At the height of 26 feet the barnacles are found attached to the rocks. Other localities might be mentioned, but there is nothing specially interesting about them.

All these fossils except the two new species are the same as the living shells, etc., which are found on our eastern shores. The fossil species are generally larger than the living, and correspond better with the species living in eastern Maine and New Brunswick. This fact shows that the climate must have been colder when the fossil species flourished than it is now.

In the St. Lawrence valley, 67 species of marine invertebrates have been found fossil. All of these, except four or five species belonging to the deep water deposit, are known as living species

in the Arctic regions of the Atlantic. found in the drift of Great Britain.

About half of them are

TERRACES.

Alluvial terraces are those banks of loose materials, generally unconsolidated, which skirt the sides of the valleys about rivers, ponds and lakes, and rise above one another like the seats of an amphitheatre. Fig. 11 represents an ideal section of a terraced

FIG. 11.

Ideal Section of a Terraced Valley.

valley, showing the relative position of the unmodified drift, sea beaches and terraces, the whole resting in a basin hollowed out of the older rocks. As we rise from the river, its immediate bank or meadow forms the lowest and latest terrace, A, which may be increasing from year to year. On the margin of the meadow we come to a steep slope whose top, B, forms the second terrace. Very frequently the lower part of this second terrace is composed of clay, and the upper part of sand or fine gravel. Another steep slope carries us to a third terrace, C, which is usually of coarser materials. A fourth terrace, D, is still coarser, and the top less level. D very often runs into moraine terraces. Rising above this, we come to the sea beaches, E. These are generally at a great distance from existing rivers, though upon the general slope facing a stream. Highest of all we come to the coarse unmodified drift, F, and finally to the solid rocks, G.

This figure illustrates the fact that the drift underlies all the beaches and terraces, although it appears upon the surface at a higher level. The beaches underlie the terraces, and each higher terrace underlies each lower terrace. We see, too, that on the opposite side of the valley we may or may not find terraces. If so they rarely correspond in number and height on both sides.

Lateral terraces are the most common and are those which are parallel to the course of the valley, and often continue for miles along its sides. Della terraces are the accumulations which have been formed at the mouths of streams, whether the junction of a tributary with the main stream or the meeting of the river and

lake or ocean. They are seen only where the land has risen since their deposition.

Terraces are not very abundant in Maine, although they are suf ficiently common to excite attention. They are often chosen for the sites of villages or of tasteful private dwellings. All the large rivers of the State are lined by them more or less. We have seen them upon the Piscataquis, Saco, Presumpscot, Androscoggin, Kennebec, Penobscot, St. John and St. Francis rivers. They are well developed in Berwick, Brunswick, Waterville, Lewiston, between Bangor and Lincoln on the Penobscot, on the east branch of the same river between Nickatou and No. 4, and upon the St. John river between the mouth of Little Black river and Woodstock, N. B. There are scarcely any terraces upon the St. John above Little Black river, and none on the Alleguash river except near its mouth. We think the terraces on the St. John the most perfectly developed of those in any valley in the State. It is a curious fact that the Acadians have settled on this river no farther up the stream than the terraces extend, and now their emigrants settle upon the Eagle Lakes rather than ascend the river higher.

BEDS OF MARL.

Two substances are commonly called marl, the calcareous and the siliceous marl. Although these substances greatly resemble each other, their chemical condition shows them to be entirely dif ferent. One is nearly pure carbonate of lime, and the other is nearly pure silica. The former is the most valuable.

The calcareous marl is largely composed of the shells of molluscous animals such as snails and clams. It is forming every day at the bottom of ponds from the accumulation of these shells, and perhaps also deriving part of its material from the chemical precipitation of lime held in solution. It is generally a fine white powder. It may be found around the edges and at the bottoms of certain ponds and lakes. When the pond has become filled up so that the water has disappeared, vegetation may accumulate over the marl and conceal it from view. The genera of shells whose remains constitute so large a portion of the marl are Cypris, Lymnaea, Valvala, Cyclas, Planorbis, etc.

It is essential for the production of marl that the prevailing rock of the region underlying the alluvium should contain a certain per cent. of carbonate of lime, for the animals cannot exist without

the means of procuring the substance of their shells. The rocks most favorable seem to be those which contain only a small per cent. of lime; at least it is so where we have made observations on the subject. Hence we need not expect to find marl in a granite region.

Marl beds have as yet been discovered only in small amount in Maine. The beds known to us are all in the northern part of the State. There is a large bed of marl near Ambejijis Lake, north of the west branch of the Penobscot. A long expanse of bog occurs at one end of the lake, and this is underlaid by beautiful white marl of unknown thickness. It lies between this lake and Millinocket, where the marl appears again. We discovered marl in the south part of Fremont, on Elijah D. Robinson's tract. It was at the south end of a bog six miles long, extending into Presque Isle, and it is not unlikely that it may be found beneath the whole of the bog, or at least in several different places in it. The marl where we examined it is mostly pure white, and is full of shells. The following species are very common in it: Cyclas similis, Say, a Lymnaea, Pisidium dubium, Gould, Planorbis campanulatus, Say, P. bicarinatus, Say, and P. parvus, Say. The portion of the marl we saw covered about sixty acres, and would average eight or ten feet deep. The gentleman owning the land north of Mr. Robinson's informed me that the marl appeared on his land also. Marl is found also in Lyndon; and just over the State line, in Canterbury, N. B., we found a fine bed of marl, containing the same shells as in Fremont. A bed of impure marl has been noticed in St. Albans, in Somerset county.

The siliceous marl is composed entirely of the skeletons of microscopic animals and plants. Like the mollusca the animalcules and plants live in the pond, and it is only their imperishable remains that collect on the bottom and form the polishing powder. It is surprising that the skeletons of microscopic animals, requiring thousands of millions to form a cubic inch, should yet form deposits of considerable extent. In Bohemia, there is a wide-spread deposit 14 feet thick, every cubic inch of which contains 41,000,000,000 skeletons of a microscopic plant. The smallest animalcule is only the 24,000th part of an inch in length, and a single skeleton weighs only 187 millionth part of a grain; 500 millions of them could live in a drop of water.

In Newfield, there is quite an abundant supply of this siliceous

infusoria. Other beds occur beneath peat beds in Limerick. We explored a large bed of it in Chalk Pond, which lies partly in Beddington and partly in No. 22, on the line of Hancock and Washington Counties. About 20 acres are underlaid with it. It is of a beautiful white color. Another bed is in a pond in the south-west part of Calais. Like the calcareous marl, this siliceous infusoria will probably be found in scores of towns as our knowl edge of them increases.

Having dwelt thus largely upon the phenomena of Surface Geology, we will now briefly state our theory.

Theory of Surface Geology.

We believe that since the tertiary period the whole of Maine, and with it all the northern part of North America, has been depressed under the ocean at least as high as the top of Mt. Katahdin, or 5,000 feet lower than it is now. Subsequently the continent rose gradually to its present altitude; and while the country was being drained, all the deposits described above were produced. Drift was principally produced by icebergs and glaciers conjoined, both when the continent was sinking and rising again. The forms of modified drift were produced largely by the aid of rivers and currents. All the agencies which operated dur ing these periods are still acting in some portions of the continent. Let us look at the condition of the continent during each period of the alluvium.

The Drift Period. As soon as the continent was submerged, northerly currents brought icebergs over its northern portions, which greatly lowered the temperature. Consequently glaciers would form on mountains comparatively low, reaching to the ocean, as now in the Arctic Zone. The enormous icebergs moving southerly would grate powerfully upon the bottom of the sea, smoothing, scratching and breaking off fragments from the prominent hills and ledges beneath, and leave a stoss and lee side upon them. To account for the transport of materials to higher levels, we may suppose that as the land sunk the stranded ice would be lifted higher and higher along the shores, and finally be urged upon and over mountains, carrying detritus along with it..

When the continent was at its lowest depth, only one or two small islands would remain. During this submergence only icebergs could act upon the rocks. When the mountains appeared