202 PREHISTORIC EUROPE. 



manner as other erratics, and some of these are veined with 

 boulder-clay. More than this, wide stretches of the coal-bearing 

 strata appear intercalated in the glacial deposits as if they 

 formed part and parcel of one and the same series, in which 

 position they have actually been mined. Similar phenomena 

 characterise the glacial deposits of Mecklenburg-Schwerin, as 

 described by Professor F. E. Geinitz. He tells us that so large 

 are some of the erratics of chalk which occur in the boulder- 

 clay (BlockmergeT), that they were at one time mistaken for 

 protruding hillocks of the rock in place. Further examination 

 of this province has proved that the Cretaceous strata are often 

 much broken, disturbed, and displaced — the boulder clay appear- 

 ing as if interstratified with the chalk in such a manner that a 

 boring-rod passed down through the Cretaceous rocks would go 

 through alternating beds of chalk and glacial deposits. Many 

 borings in the chalk of the Diedrichshagener Bergen have proved 

 that the Cretaceous strata there are underlaid by boulder-clay, 

 and are thus themselves only a gigantic boulder. They have 

 been pushed out of place, and dragged forward by the ice. 1 

 Professor H. Credner, in a most instructive paper, has recently 

 described many similar appearances in connection with the 

 boulder-clay of Saxony. He shows that frequently the Silurian 

 rocks are broken and ruptured, and the resulting cUhris enclosed 

 in the lower part of the boulder-clay. The sections he gives 

 as illustrations of this are sufficiently remarkable, but the most 

 striking examples of disruption, contortion, and displacement are 

 supplied, he says, by the Brown Coal formation (Oligocene). 

 Boulder-clay and glacial gravel are confusedly commingled with 

 the brown-coal beds, the latter being often crumpled up and 

 contorted, and so squeezed that long tongues are seen protruding 

 into the boulder-clay. The same phenomena, he shows, are 

 characteristic of the gravel-beds associated with the till — they 



1 Beitrag zur Geologie Mechlenlurgs (Neubrandenburg, 1880), pp. 20, 39. For 

 another interesting example, see Boll's description of the bed of chalk near 

 Malchin, in Mecklenburg. This layer is some 35 feet in thickness, and rests 

 npon a dark-coloured boulder-clay, which has been pierced in borings to a depth 

 of 43 feet. Geognosie der deutschen Ostseelander, 1846, p. 136. 



