Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/165

1872.] JONES AND PARKER — CRETACEOUS FORAMINIFERA. 131 same species. "When out of some thousands of specimens of Operculina, say, a dozen pronounced forms had been selected, such as by themselves seemed well marked and distinct, it might turn out that after all there was but one species present, with intermediate varieties connecting all these different forms. He thought the same held good with Rotalinoe, and that there were osculant forms which might connect, not only the species, but even the genera into which they had been subdivided. This fact had an important bearing on their genetic succession, especially as it appeared that some of the best- marked types were due to the conditions under which they lived.

The temperature in tropical seas differed in accordance with the depth so much, that when 2000 fathoms were reached a degree of cold was attained such as was to be found in high latitudes ; and in consequence the deep-sea forms in tropical latitudes assumed the dwarfed character of those in shallower seas and nearer the Pole. He suggested caution in drawing inferences from forms so subject to modification, both spontaneous and due to the depth of the sea, especially as connected with abundance of food.

Prof. Ramsay remarked that geologists would be pleased to find Foraminifera exhibiting, like other organisms, changes in some degree connected with the lapse of time. These low forms, however, could hardly afford criteria for judging of the age of geological formations, while at the same time such ample means were afforded by the higher organisms for coming to a conclusion. He cited, for instance, the Cephalopoda as proving how different were the more important forms of marine life in Cretaceous times from those of the present day. He thought that no one who had thoroughly studied the forms of ancient life would be led to ignore the differences they presented, as a whole, from those now existing.

Mr. Seeley, Dr. Murie, and Mr. Hicks also made some remarks on the paper.

Prof. Jones, in reply, observed that the question of whether the Foraminifera in a given bed were derived or not was to be solved partly by their condition and partly by their relative proportions, and that in most cases sufficient data existed on which to found a judgment. He agreed with Dr. Carpenter as to the existence of extreme modifications ; and it had been his object to ignore such as seemed due to ordinary and local causes, and to group the forms in accordance with certain characteristics. Whether the classification was right or wrong, it was necessary, for the sake of increasing knowledge, that fossils of this kind should be arranged in groups ; and whether these were to be regarded as truly generic was a minor consideration. In forming their types and subtypes the authors had carefully avoided minor differences ; and they thought that the modifications which were capable of being substantiated were significant of a great lapse of time. A variation once established never returned completely to the original type. In Globigerina, he stated that there were in Cretaceous times 8 forms, in Tertiary 12, at the present time 14 ; and these modifications he regarded as equivalent to the specific changes in higher animals.