100 MAPS AND TEEKACES. 



MODE OF REPRESENTING THE TERRACES AND BEACHES UPON MAPS. 



Upon the general map of the Surface Geology of Vermont, Plate II., we have attempted to exhibit the 

 principal terraces by means of colors. Many smaller ones, however, are omitted ; nor is the true 

 width of the terraces given with great accuracy. The map is so small, that the surface which a terrace 

 covers would not generally be large enough to represent the terrace at all ; hence the width on the map is 

 exaggerated, except where the terrace is very large. To give these phenomena with absolute aceuracy, 

 would require a great amount of labor in observation, which would be useless unless the details could be 

 represented upon a map say twelve feet long for the whole State and the Legislature would hardly think 

 the value of the map sufficiently great to incur the expenses of its publication. Nevertheless, though an 

 exaggerated scale may be generally used, the proportions of the terraces to one another are preserved, as 

 nearly as possible ; and the proportional variations in width, &c. on the map, are truly delineated. Besides 

 general map we have given several local maps of the terraces, &c. These, being projected upon a 

 larger scale, may be regarded as correct representations. We would gladly have enlarged the number of these 

 local maps, not only from their great value to science, but also for the use of the inhabitants of the 

 various villages, where the phenomena of surface geology are developed. 



All the streams, it will be observed, are not marked with terraces. This is because we have not had 

 opportunity to visit them all for this purpose. The principal deficiency is on the Missisco River ; but the 

 loss is partly compensated by the fact that the terraces are not as strikingly developed there as else- 

 where. The map of the surface geology of Connecticut River, upon Plate III., is perhaps the most valuable 

 contribution to science of the whole. It was reduced from a large map over thirteen feet long. 



We are now able to map the terraces from the mouth to the source of Connecticut River, by combining 

 with Plate III. of Hitchcock's Illustrations of Surface Geology. This is the first time, we believe, 

 Plate III. in the history of Geology, that the alluvial deposits of so large a river have been as fully 

 delineated. We did not represent the Surface Geology of Connecticut River upon Plate II., because it would 

 have been a useless repetition of Plate III. We have the materials for similar maps of the Winooski and 

 Lamoille Rivers, besides some of the larger tributaries of the Connecticut, but they are not engraved 

 because of the expense. 



The colors on all the maps are the same for the same terraces, reckoning upward from the river. The 

 lowest meadow is considered the first terrace, the next higher the second, and so on ; hence it follows that 

 the same color does not always represent terraces of the same height, since they vary in this respect on dif- 

 ferent streams ; and in general, the size and height of the terrace correspond to the size and height of the 

 river. 



In all the references to the terraces in this report, we shall designate them as No. 1, No. 2, &c., counting 

 them at every place where the largest number is found to occur. Sometimes several terraces, especially those 

 designated as No. 2 and No. 3, are wanting when we say that Nos. 1 and 4 are present at this particular 

 locality, because the terrace called No. 4, a mile distant, continues unbroken to this spot, while the others have 

 been worn away. While we cannot represent the terraces of the same height, upon different streams, by the 

 same color, we endeavor to represent the terraces of the same height upon their own stream with the same 

 color, so far as an equable height is maintained by the terrace itself which is not always the case. 



Upon a few streams that -descend rapidly, what we shall presently designate as the Lateral and Delta 

 terraces, are rarely partially combined as upon the Whetstone Brook that empties into the Connecticut 

 River, in the village of Brattleboro. A similar very marked case is described in the Illustrations of Sur- 

 face Geology, and figured upon one of its plates (Plate VI., Fig. 2.) It is' stated that in Pelham, Mass., upon 

 Fort River, there are thirteen terraces, each one higher than the preceding, but the thirteenth is no higher 

 above the river opposite to it than the fourth opposite to the same stream. If, then, we should estimate the 

 terraces upon Whetstone Brook by calling every one that is found at a higher absolute level an additional 

 one, we might run up to twelve or fourteen, while the fourteenth above Connecticut River would really be 

 the fourth above tke brook in West Brattleboro. 



