THE PHYSICAL FEATURES OF CENTRAL MASSACHUSETTS. By WILLIAM C. AIDEN. INTRODUCTION. The area described in this paper lies mainly in central Massachu­ setts and comprises about two-thirds of the plateau extending from the eastern part of the Connecticut Valley on the west to the low­ lands of Middlesex County on the east (fig. 1). The area is about FIQDBE 1. Map showing location of the Holyoke, Ware, and Quinslgamond quadrangles, central Massachusetts. 52 miles in exstent from east to west and 35 miles from north to south and includes approximately 1,835 square miles. It lies between parallels 42° N. and 42° 30' N. and meridians 71° 30' W. and 72° 30' W. and thus includes on the south a strip of northern Rhode Island about half a mile to a mile wide and a strip of northeastern Connecticut about 2 to 2£ miles wide. In the years 1885-1887 a topographic survey of the Belchertown, Barre, Worcester, Marlboro, Palmer, Brookfield, Webster, and Black- stone 15-minute quadrangles was made by the United States Geologi- 92818° 25 2 13 14 COJSTTEIBUT10NS TO GEOGRAPHY OF UNITED STATES, 1923-1924. cal Survey, and maps of these quadrangles were published on a scale of 1:62,500, or approximately 1 mile to the inch, with a 20-foot con­ tour interval. In 1908 these maps were combined into two covering the same area on a scale of 1:125,000, or approximately 2 miles to the inch, with a contour interval of 40 feet. The two 30-minute quad­ rangles thus mapped were designated the Ware and Quinsigamond quadrangles. These maps are combined .in the present paper (PL VI, in pocket) to show the physical features.1 The writer's examination of the surficial geology of this area was designed to be supplementary to the work of Prof. B. K. Emerson, who had for a long time been studying the deeper-seated hard-rock formations. The material included in the present paper was gath­ ered in the summers of 1906 and 1907 and was originally prepared for publication with the results of Professor Emerson's studies in folios of the Geologic Atlas of the United States and was submitted, for examination and criticism, not only to Professor Emerson but to Profs. T. C. Chamberlin, W. O. Crosby, and J. H. Perry and later revised. To these gentlemen the writer wishes to express his appre­ ciation for numerous suggestions. Professor Emerson had previ­ ously published the results of his own studies of the western part of this area and of the Holyoke quadrangle, which lies immediately west of the Ware quadrangle.2 To these publications and to personal conference with Professor Emerson the writer is much indebted. Considerable material has also been obtained from publications of other authors, as cited elsewhere in the text, particularly the " Physi­ cal geography of Worcester, Mass.," by J. H. Perry. Professor Emerson's " Geology of Massachusetts and Ehode Is­ land " 3 includes a brief description of the glacial and lacustrine phe­ nomena of the Ware and Quinsigamond quadrangles and adjacent areas. Some material was prepared by the present writer during the World War for incorporation in a description of the country around Camp Devens, by W. W. Atwood, printed on the back of the Camp Devens topographic map, which covers parts of the Worcester, Marl- boro, and adjacent quadrangles. It is realized that publication so long after the time of the original studies, without reexamination of the field, incurs the risk of some anachronisms of description. It is hoped, however, that these will be found not to be serious. The elements of human history, such as t Such later features as the Wachusett Reservoir and changes due to its construction, enlarged towns, and the newer roads and electric railways are not shown on the 15-minute maps, but they show considerably more topographic detail than, the Ware and Quinsigamond maps and are suitable for class and field use. All these maps are for sale by the Director of the United States Geological Survey, Washington, D. C., at 10 cents each, or 50 for $3. 2 Emerson, B. K., Geology of old Hampshire County, Mass.: U. S. Geol. Survey Mon. 29, 1898; U. S. Geol. Survey Geol. Atlas, Holyoke folio (No. 50), 1898. U. S. Geol. Survey Bull. 597, 1917. PHYSICAL FEATURES OF CENTfiAL MASSACHUSETTS. 15 the settlement of the region by the whites and its commercial develop­ ment, are not treated in this paper. For these subjects reference should be made to other sources, among which may be noted a pam­ phlet on the geography of Worcester, by Robert M. Brown, formerly of the State Normal School, who treats in an elementary form adapted to class use certain of the phenomena described in the present paper. ORIGIN AND HISTORY OF THE CENTRAL MASSACHUSETTS UPLAND. THE CRETACEOUS PENEPLAIN. An observer standing on any portion of the upland of central Massachusetts that affords an extended view is struck at once with the remarkable uniformity of the horizon line (PL VIII, A). As he gazes in all directions and notes the general correspondence of upland and ridge crests, he is impressed with the idea that were the valleys filled up to the level of the summits of the ridges the whole would constitute a nearly uniform plain sloping gently toward the southeast and with but few elevations rising above it. The mineral composition and the attitude of the closely crumpled rock formations now exposed at the surface in this region (PL IX, B) are for the most part of the types that are generally associated with the internal structure of mountain folds and are developed only at great depths below the surface of the earth, and it is therefore evident that the exposure of these formations must be due to the removal of great thicknesses of overlying rock. In consequence New England has been called a " worn-down mountain region." 4 The removal of this material was accomplished principally by the ordinary processes of rock weathering or decay and stream erosion, such as are going on about us every day. The upland represents an ancient land surface developed through long-continued wearing down, which reduced most of the preexisting land forms to a plain gently sloping to the sea. Such a surface is called a peneplain that is, almost a plain. Valleys were broadened and mountains, hills, and ridges were cut away until but few portions of the former elevated tracts remained. The most notable of the remnants of higher levels still persisting in the area under consideration are Wachusett Mountain (PL VIII, B) , Little Wachusett, and Asnebumskit Hill. Farther northwest, in New Hampshire, stands Mount Monadnock, the typical representative of such topographic features, to which its name (monadnock) has been given.5 The wearing away of the ancient mountain ranges * Davls, W. M., The physical geography of southern New England, In The Physiography of the United States: Nat. Geog. Soc. Mon., p. 280, 1896. B Davis>, W. M., The improvement of geographical teaching: Nat. Geog. Mag., vol. 5, p. 70, 1893. 16 ' CONTRIBUTIONS TO GEOGRAPHY OP UNITED STATES, 1923-1924. required an exceedingly long time many thousands or millions of years. An account of the formation and destruction of these moun­ tains of long ago is not attempted in the present paper, nor are the dim vistas of yet remoter ages penetrated. The description begins at the time when the mountains had gone and the peneplain had been developed. The detritus from the long-continued erosion of the land was swept by the streams into the bordering seas, forming sedimentary strata. The fossils now found embedded in these strata are forms that lived in the Cretaceous period, and the ancient land surface is therefore known as the Cretaceous peneplain. To visualize this ancient peneplain it is necessary, as indicated above, to imagine the depressions filled up to the level of the intervening ridge crests, for the peneplain is now largely dissected by valleys ranging'in depth from 100 to several hundred feet. Moreover, most of the valleys give evidence of having been partly refilled since they were cut. As such dissection of a worn-down land surface is accomplished only in consequence of uplift sufficient to give to the sluggish streams the renewed energy resulting from increased fall, it is concluded that the peneplain has been raised to its present position since its de­ velopment. As shown in Figure 2, most of the higher portions of this peneplain are in the north-central part of the area, northeast of Worcester and north of the main line of the Boston & Albany Railroad. Here great tracts stand from 900 to 1,300 feet above sea level. Smaller tracts at nearly the same general altitude extend the high belt southward from Warren into the eastern part of Hampden County and Connecticut. From this axial zone the general upland slopes from 900 to 500 feet above sea level in a southeasterly direc­ tion toward Rhode Island, and to about 400 to 600 feet in an east­ erly direction, to the borders of the lower Nashua, Assabet, and Blackstone river basins in eastern Worcester County. The high portions (900 to 1,300 feet above sea level) are also extensively pre­ served north of Belchertown and west of Middle Branch of Swift River. Prior to the uplift in late Cretaceous time the peneplain was probably continuous throughout this region and extended westward across what it now the Connecticut Valley lowland. It has been pointed out by Barrell 6 that the surface descends from the higher altitudes in southern New England toward the coast not by a simple regular slope but by a series of steps.