Two notes on the isotopic constitution of carbon in minerals

Measurements of the $\text{C}{}^{12}\text{C}{}^{13}$ ratio on two generations of calcite and the matrix from a single specimen are given and discussed. This ratio has also been determined for four examples of graphite and limestone occurring together. The formation of the graphite is briefly discussed in relation to the $\text{C}{}^{12}\text{C}{}^{13}$ ratios.