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[[underline]] 1892 [[/underline]] [[underline]] November 20. - continued. [[/underline]] bles that of Point of Rocks on the Appomattox. Like the latter, too, it contains quartz pebbles well worn and rounded. Kaolinic clay balls occur in this sand and also those of dark, buff, and pink clay. But most remarkable of all is the presence of precisely similar pockets of green sandy clay indistinguishable from that of the marine Tertiary. If these are really Tertiary the sands cannot be of Potomac age, and yet I have to-day collected specimens of it from the lowest of these beds and solidly in place. Their occurrence is exactly like that observed in Richmond. In fact the way in which, throughout this series of beds, the glanconitie greensands and clays are found intermixed with the Potomac sands is a perpetual puzzle. [Basal Potomac Clay as at [[Locksmith?]] Point] [[end page]] [[start page]] [[underline]] November 24. [[/underline]] Excavations are now in progress on 16th St. extended and new features have been laid bare. I went there with Prof. Fairchild and Mr. White and we all made a study of it. They have cut down to the Archean and exposed the overlying materials. I had formerly supposed the variegated clays of the Potomac to be present here, having found them in the sides of the former cutting. It now appears that they occur only in pockets in the greatly disturbed mass otherwise similar the other at Weslay Heights and many of the places along the Archean border. Some doubts, however still remain which may be removed by further operations. From here we went to the exposure on 17th St. extended, previously visited by Dr. Hollick and myself. This seems to consist of the same materials. The clay pockets are smaller and the clay mostly white A reddish cross-bedded sand include them. [[Cobble?]] lies in streaks through some [[fiarts?]]
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