IOO THE HABITAT OF THE EURYPTEKIDA 



buried; but in eastern New York during the later stages of the Ordo- 

 vicic the streams did not have a moderate gradient. The elevation 

 of the land leading up to the tectonic movement known as the Taconic 

 folding which displaced the rocks in some regions in the Hudson 

 Valley as much as 90 was in progress at least throughout the 

 Upper Ordovicic. One of the results of this movement was the 

 steepening of the gradients of the streams which thus became tor- 

 rential, not necessarily through increased rainfall, but through in- 

 creased gradient. The streams consequently brought great quantities 

 of clastic material to the margin of, and into the sea, where deposi- 

 tion probably went on in a sinking geosyncline. 



Summary. The physical characters of the Normanskill and 

 Schenectady beds point to Appalachia as the source of the sediments. 

 The mode of occurrence of the eurypterids, graptolites and plant 

 remains is better explained on the hypothesis that the eurypterids 

 and perhaps the plants also were fluviatile and not marine organisms. 

 As yet the Ordovicic merostome faunas are too little known to say 

 that the habitat can be proved to be one or the other; the most that 

 we can say is that all the known facts are better accounted for by 

 the fluviatile hypothesis, which is fully supported by the palaeonto- 

 logical and chorological data. 



3. THE SHAWANGUNK CONGLOMERATE 4 



In the intercalated shales in the Shawangunk conglomerate at 

 Otisville, Orange County, New York, and at the Delaware Water 

 Gap and elsewhere a large eurypterid fauna has been discovered. 

 The Shawangunk is distributed in the form of a semi-cone, having 

 its greatest thickness, about 2000 feet, in the Delaware Water Gap 

 region, and thinning away in all directions. That is, it has the form 

 of a dry delta or alluvial fan rather than of a sea coast deposit, for if 

 it were the latter, it would be of fairly uniform thickness and would 

 not have the semi-cone shape. The pebbles in the conglomeratic 

 portion of the Shawangunk are well rounded, but in some sections a 

 certain amount of angularity is still retained as a rule. For river- 

 worn pebbles to be perfectly rounded, they must be transported for 

 a considerable distance. Again the complete destruction of all but 

 the quartz argues for prolonged transportation and frequent rework- 

 ing. As in the case of the other elastics, there was no source for the 



4 The lithogenesis of this formation has been discussed in such detail by Grabau (Early Palaeo- 

 zoic delta deposits) that it is unnecessary to give more than a summary here. 



