GEOLOGICAL DEVELOPMENT.

BY JUSTIN E. BURBANK.

THE territory of our state is not extensive in comparison with that of many others. A little over nine thousand square miles is all that New Hampshire can call her own. This does not allow her the privilege of boasting of her imperial domain. Her length is one hundred and eighty miles, her average width fifty-two miles, covering a little more than two and one half degrees of latitude, and less than a degree of longitude.

Within these somewhat narrow limits is included a great variety of surfaces and of soils, and much diversity in respect to climate and altitude. The elevation of the different localities within the boundaries of the state rises from the level of the sea to six thousand two hundred and ninety-three feet. Almost every foot of this variation is represented by the height of some particular area of land.

In climatology, also, great differences manifest themselves. From the highest mean annual temperature of 48° Fahrenheit, the mercury sinks in the coldest region to 25° for the yearly average. Mountain and seashore are ours without passing any state line. The roar of the Atlantic and the raging tempest on the top of Mount Washington may both be experienced by the traveler on the same day without crossing over any foreign soil. No other state in our Union, probably nowhere in the world, contains so great diversity in so little space.

At first we are inclined to group all these conditions together, and represent them as springing out of the physical geography of

the state.

But the physical geography of any specified territory rests upon its geology as a foundation.

Geological development in its final fixed result determines the main features of the geography of a country. Geological influences were at work far back in the history of material things, and carved out the continents as they now exist, fixed the bounds of ocean at its present shore, dotted the sea with islands, and adorned the landscape with silver streams that conduct along their highways the returning waters to their natural bed. We cannot trace matter back to its original creation, and see it in its primeval form launched into existence. Human knowledge has a limit put upon it. Clouds of eternal mystery rest upon some things, and it is vain for us in our blindness to endeavor to remove or to penetrate them.

The study of the scientific geologist, nevertheless, devoted to the hardened surface of the earth, is able to infer with some degree of certainty, that there was a period when what we call the solid rock was in a state of fusion, or at least in a plastic condition, through the influence of heat, and that then it took the shape which it now presents to us, and cooled into its apparently unchangeable form. Further back than this, science furnishes no guide, and conjecture is essentially of no value in such a field.

From the shape our rock-ribbed state has assumed, we may infer some of the laws of the forces which raised its surface from out the unseen depths. The power that brought the White Mountains from below would appear to have been applied in a lateral direction, and, subsequently, the ridges raised by this force were subjected to some mighty propelling influence, acting in a direction nearly at right angles with the first. We cannot determine whether it was steam or expanding gases, or mighty solid bodies coming into collision, and in their mutual crash raising some masses and depressing others, breaking some accumulations of matter and driving others together. All such conflicts were pre-historic, and probably anterior to animal or vegetable life. The varied action of these spent forces has left as a legacy for our contemplation and study a surface geology of as much interest as any upon the face of the globe.

In the application of geology, as far as it has become a trust

worthy science, the leader in the late state survey has accomplished a work of no small value to the student who is interested in acquiring knowledge, and to the native of our soil, who loves the place of his birth, and who desires to thoroughly understand all that appertains to it, because it is his own home.

New Hampshire is geologically as old as any land on this continent. It belongs to what is styled the Eozoic period, the earliest of the four great periods into which the geological era is divided. Though the term, through its etymology, indicates the dawn of life, the lower division of the Laurentian section is azoic, or without life. This embraces the porphyritic gneiss that is so common in the elevated ridge that divides the valley of the Connecticut from that of the Merrimack.

This land, the first to appear within our limits, rose out of the wide-spreading ocean in the shape of islands, about thirty in number, of a variety of sizes and forms. The largest was somewhat irregular in its outline, and reached from Groton, on the north, to Jaffrey, in the south. In its widest portion, it extended from Hopkinton, on the east side, to Washington, on the west. The northern and southern portions were much narrower, creasing each to nearly a point.

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The most easterly example of this porphyritic gneiss formation was, at the commencement of this primitive period, a very limited area in the town of Seabrook, touching the Atlantic Ocean, bordering on the state line, where, in its sublime solitude, it looked forth upon the waste of waters and beheld nothing but desolation in the midst of the billowy sea, the nearest land being another small island in what is now the town of Pelham. The most northern land was in the town of Whitefield. The White Mountains, except a small portion in the town of Franconia, do not

appear.

The highest summit reaches an altitude of 4,300 feet. In the Groton and Jaffrey area, the greatest elevation is seen in Mount Lovewell, 2,487 feet, and Mount Sunapee, 2,683. This area, at its western limit, coincides mainly with the dividing elevation between the valley of the Connecticut and that of the Merrimack.

The above sketch shows the dry land of New Hampshire at the close of the Laurentian period. The succeeding Montalban.

period of the Eozoic era presents an addition of a much larger area to the extent of the state. At the close of this period nearly two thirds of it were out of water. The eastern boundary was a line between Dover and Lake Umbagog. The southern boundary was a line between Hinsdale and Brookline. The southeast limit of the development of this period and the preceding one was a nearly straight line connecting Brookline and Dover. The western limit was a line nearly parallel with the Connecticut river, distant from it about the width of one line of towns, and reaching from the Massachusetts boundary to Haverhill. The northwestern limit was a nearly straight line across the state diagonally from Haverhill to Lake Umbagog.

The Montalban formation seems to be joined to the Laurentian as to a nucleus. It includes several different varieties of the gneiss rocks, as the Bethlehem group, the lake gneiss formation, the White Mountain and the Franconia groups. Within this last are included the granites of Concord, Plymouth, and many other towns in the state, which are very valuable for purposes of architecture and of art. The entire area gives abundant proof of metamorphic action.

The study of these rocks in all their rich variety gives rise to many an interesting problem, which the geologist must study carefully in order to arrive at a satisfactory solution.

The Labrador, the next period, is marked by the breaking forth of liquid masses of molten matter, produced by subterranean heat, and ejected, without doubt, in consequence of some depression in the surrounding solid masses of the preceding period. This melted matter, on cooling, constituted the granite and syenite that include a part of the White Mountains and an extensive range of territory between Franconia and Conway. The Labrador period, while it produced such important changes, did not add largely to the extent of the land of New Hampshire. The period following this was the Huronian, and without doubt the dry land of the state assumed during its continuance a settled, solid condition, and may have been covered with a light clothing of green vegetation. It was the era of the deposit of the precious metals of New Hampshire, and of some other minerals.