JOURNAL 

 The New York Botanical Garden 



Vol. VIII. November, 1907. No. 95. 



THE BOULDER BRIDGE. 

 The bridge built during the last year on the site of the old 

 wooden structure across the Bronx River at the northern end of 

 the hemlock grove, was completed in September, under the con- 

 tract awarded by the Commissioners of Parks on October 18, 

 1906, to M. J. Leahy. It consists entirely of boulders, selected 

 from old stone walls, and unearthed during grading operations ; 

 very nearly all these stones are trap-rock (diabase), brought by 

 the glaciers of the ice-period from the Palisades of the Hudson, 

 which lie directly in the line of the glacial movement, as evidenced 

 by grooves cut in the ledges of gneiss and schist, so abundantly 

 exposed in parts of the Garden grounds and beautifully illustrated 

 on the ledges along the western side of the valley of the herba- 

 ceous garden, where a path has been laid so as to cross one of 

 these exposures. At this point the direction of the glacial 

 groovings is seen to be a few degrees to the east of south, and 

 this line continued northward would strike the Palisades about 

 opposite Yonkers. These trap-rock boulders are the most 

 abundant large stones in the glacial drift of Bronx Park and the 

 surrounding country, and in places they are exceedingly numerous, 

 so abundant in fact as to make grading operations difficult and ex- 

 pensive. During our first grading work we hauled a great many 

 Qf these boulders into low grounds which had to be filled, but 

 it occurred to us several years ago that' a bridge might be built 

 of them, and Mr. John R. Brinley, landscape engineer of the 

 Garden, made astudy for such a structure, which was subsequently 

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