Of special interest is a third series of piles, which he describes as terminating in the sea-sand underneath all. These piles were five in number, four oak and one birch, 2 to 5½ inches in thickness, and 18 to 33 inches in length. They were placed in a zig-zag fashion about 1½ foot apart, and traced through the layer of "Kuhdünger" to the "Packwerk," where they became so rotten as to be no longer recognised. One of them had also a hole, which still retained portion of a projecting spar. Our investigator made observations, but of a much more limited character, on nine other _Wurthen_, and in all of them he found the "Packwerk" to be a special feature in their structure. Such is an epitome of the facts on which Dr. Hartmann bases his opinion that not only the _Wurthen_, but also the neighbouring _Warfen_ and _Terpen_, were constructed like the fascine islands of prehistoric Switzerland, and the Scottish and Irish crannogs. The idea of pile-buildings can scarcely be entertained by him, and he stoutly combats Pigorini's opinions in regard to the _Terpen_ of West Friesland. The Fahrstedter Wurth, according to Hartmann, consisted of an original mound some seven feet high, to which on two subsequent occasions additions were made. The initiatory process of its construction was to form a basis of _Kuhdünger_ two feet in thickness. Over this clay and rubbish were placed, to the extent of other two feet; and then came the fascine structures, which raised the mound other three feet. To keep the mass together, piles were driven here and there down to the sandy bottom. But the inhabitants soon found that this was too low to shelter them from the waves and floods, so they constructed an addition to their mound, which raised its surface to ten feet. But this was not enough, and so a third addition was made, which added six feet more to the mound. At this height its surface would be about twenty feet above the medium sea level (_Normal Null_), and at this height Dr. Hartmann concludes that cottages would be quite secure, as the highest tides on record--viz. 4th February, 1825, reached only 12 feet 4 inches above the medium sea level, a result which would leave a considerable margin for the Fahrstedter Wurth. Of course, the tides never reach it now, as it is protected by the sea-dykes, the first of which was constructed in the middle of the twelfth century.