18. _Puddingstone._ Where Pownal Mountain reaches the Hoosack, (T) 3 miles north of the college, are some hills of this aggregate. It is composed of rounded masses of quartz, chlorite, and limestone, of various sizes, connected by an argillaceous cement. 19. _Potters' Clay._ Excellent for vessels of common pottery. The minerals of this section, it is obvious, are not very important; but as connected with a transverse section of the country, they possess considerable interest. For this reason they have been particularly mentioned. In the north part of Williamstown is a _mineral spring_, familiarly called the _Sand Spring_ (S.) The water rises from several places in a reservoir of about a rod in diameter, and from one to three feet deep. It is very soft and warm, but contains very little saline or earthy matter. Gas continually rises in it. It appears much to resemble the spring at New Lebanon, New-York, and has proved useful in the cure particularly of some _cutaneous_ diseases. The _transverse section_, connected with the map, passes over Stone Hill, and the north part of Saddle Mountain. The different rocks are shown in the section, directly below their places on the map, by drawing lines from the several strata parallel to the sides of the map. This section is connected with that given by Mr. Hitchcock, in the 2d number of this Journal. It ought perhaps to be mentioned, that according to Mr. Eaton's account, the granite of this section sinks under gneiss to the east, and rises again in Hampshire County, "supporting the same rock of gneiss;" but where it reappears, the granite contains "many imbedded minerals." This section corresponds generally to the place and character of the minerals in any section across Berkshire county. There are, however, some peculiarities which may be mentioned at a future day. The colouring corresponds to that on the geological map in Cleaveland's Mineralogy. C. DEWEY. _Williams' College, Jan. 27, 1819._