Observational facts about the local differences of geomagnetic variations are described with most emphasis on the North-German-Anomaly. The main features of a theoretical treatment of the electromagnetic induction are given in the induction curve of the model. The interpretation of the observations depends on the resistivity values of the uppermost layers. Possibilities and boundaries of the geomagnetic deep-sounding are demonstrated.

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A survey with temporary geomagnetic field stations (Askania Variographs) has been conducted in the southwestern United States in order to study local differences of geomagnetic variations. Anomalous large Z-variations, accompanied with a slight reduction of the variations in D and H, have been recorded along the California coastline for long-period (Sq) and short-period (bays, ssc's) variations. This Californian coastal anomaly has been interpreted as edge-effect of the Pacific Ocean and its effect upon the induction within the highly conductive substratum in the upper mantle, thereby allowing conclusions about the deep conductivity structure Less pronounced anomalous variations further inland in central California (Sierra anomaly) seem to be caused by conductivity differences in the continental surface layers. A third anomaly between Tuscon, Arizona, and Sweetwater, Texas (Texas anomaly), has been interpreted as a change in the deep conductivity structure which occurs along the eastern margin of the Rocky Mountains.

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Two unusual features of geomagnetic variations have now been discovered in the Arctic Archipelago of Canada. The first anomaly at Alert on Ellesmere Island is characterized by abnormally high levels of irregular magnetic activity and a persistent directional characteristic of the vector horizontal disturbance. An adequate iono-spheric explanation has not been found. Recent papers have given an explanation of the gross characteristics of the Alert magnetograms in terms of induction in a large anomalous conductor in the upper mantle striking parallel to the channel separating north Ellesmere Island from Greenland. Field experiments followed by simple potential and spectral response analyses confirm the existence of a gross conductor. In this paper the uncertainties in and shortcomings of the first-order explanation and minor modifications are stressed, and an alternative solution involving induction in the conducting mantle and a highly conducting circuit examined. The alternative solution appears to be even more inadequate.
The second anomaly at Mould Bay, Prince Patrick Island, is characterized by the striking absence of shorter-period vertical field magnetic variations. Assuming the presence of a sheet conductor at depth it has been estimated earlier from the frequency dependence of the power spectrum that a 10-20km thick layer with a conductivity near 10¹¹emu is required near the bottom of the crust or in the upper mantle. The assumptions in deriving this explanation are outlined, and theoretical curves shown which demonstrate that the neglect of reasonable conductivity above and below the anomalous layer appears justified. Results are shown applying the same technique to plane earth induction in a non-anomalous area, and to one magneto-telluric situation of current interest.

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The nature and accuracy of the deductions that can be drawn about the distribution of conductivity within the earth from surface measurements of natural magnetic variations and earth currents are considered. Both the magnetic variations method and the magnetotelluric method are based essentially on calculating the currents induced in some model distribution by a given inducing field, and adjusting the parameters of the model to make the calculated results agree with observations. But up to now only a few relatively simple problems in electromagnetic induction have been satisfactorily solved, and interpretations of observed values have sometimes been based on the solution of problems which do not adequately represent important features of the physical situation.
Global problems and local problems are distinguished and the different types of mathematical problems that arise in the two cases are considered.
Magnetotelluric profiling has been largely based on a simple theoretical model which treats the electromagnetic field as uniform over any horizontal plane and therefore ignores the nature and dimensions of the ionospheric inducing field. This is not justifiable and leads in some physically probable situations to serious overestimates of the conductivity.

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Some anomalies in geomagnetic variations observed in Italy from 1957 on, are referred about.
The main phenomenon, observed at Ponza Island (Central-Southern Italy), is characterized by an almost absolute parallelism between ΔZ and ΔH variations, during disturbances shorter than two hours.
In its larger evidence, this phenomenon is limited at Ponza Island and it attenuates rapidly when approaching the opposite Italian coast: it vanishes almost completely at L'Aquila Observatory (Central Italy) and Mt. Capellino (Genoa).
Instead, an effect of antiparallelism was observed at Frontone (North Italy) while operating a temporary station installed there in the occasion of the Solar Eclipse of February 1961.
A further investigation has been performed recently on S_q variations.

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The coast effect [CE] means an influence of the boundary of two different by their electromagnetic characteristics, mediums-land and sea-on the alternative electromagnetic fields.
Here are mentioned the properties of the coast effect for a wide range of variation periods from millimicrosecond up to the tenths of the minutes.
The coast effect for the variations with the periods from the units of seconds to the tenths of minutes is divided in 2 types by the look of polarization of the primary field as to the coast CE-1 and CE-2.
Here are given experimental data by CE-1 for the area of the stations Mirny (Antarctida) and CE-2 for the station Alushta (coast of the Black Sea).

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An attempt is made to interpret the magnetotelluric sounding curve at Meanook, Alberta, Canada. Records obtained during field operations in August 1961 and magnetograms and tellurograms recorded at the same time at the Dominion Observatory Meanook are analysed by a visual correlation method to obtain apparent resistivity values for periods between 10 and 3000 seconds. Several theoretical layered earth models are considered in order to fit the data thus obtained. A resistivity distribution, obtained from one of the models which gives an adequate fit to the observed data, agrees fairly well with previous resistivity estimates obtained by other investigators. A probable decrease in the resistivity between the depths 90-140km is obtained by this technique. The lack in resolving power of the magnetotelluric method to delineate various layers with moderate resistivity contrasts such as at the ‘Moho’ and at a depth of 90km is demonstrated with the help of a few resistivity models.

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